What are the common card themes used by each protagonist?

[Dread Kaiser]

I try to count out DRXD since it will go away anyway. It's not really part of his Deck, if we are honest. And if the rest of the Yus die, neither will the other Dragons. So isn't Tuning Magician (I guess?) but I think he will keep it since noone wants it and she has Magician in her name. Enlightment is his own Creation and an Evolution of his very own Magicians hence why I would call it a fitting Second ace. I'm talking about them more more as a generic Deck, not Arc specific.

Thats speculation, For all we know Yuto will stay dead/Merged or will come back and just give Yuya the dragon for the final battle A la End of 5D's

And I still can't see how you say BLS is the secondary ace, especially if you are referring to Envoy as Yugi never used it. what should qualify it as an ace is how much it was relied on, not how good it was (in-universe or out)...especially since Envoy would have been a very poor card for a protag to have. don't usually want to give the MC something so overpowered, its why Turbo warrior disappeared. but I digress

Yugi never used Envoy and the original was demoted to fodder to fuse into Dragon master knight, who then got exploded 2 of 3 times by some ancient Demon thing. I wouldn't exactly call that reliable

if you want to count alternate versions of the Monsters, then Gaia beats him out too as I do not recall Yugi ever relying on BLS to take down floatation rings
....unless you want to Count Gaia as an alternate BLS....

[Mofiz]

Thats speculation, For all we know Yuto will stay dead/Merged or will come back and just give Yuya the dragon for the final battle A la End of 5D's

And I still can't see how you say BLS is the secondary ace, especially if you are referring to Envoy as Yugi never used it. what should qualify it as an ace is how much it was relied on, not how good it was (in-universe or out)...especially since Envoy would have been a very poor card for a protag to have. don't usually want to give the MC something so overpowered, its why Turbo warrior disappeared. but I digress

Yugi never used Envoy and the original was demoted to fodder to fuse into Dragon master knight, who then got exploded 2 of 3 times by some ancient Demon thing. I wouldn't exactly call that reliable

if you want to count alternate versions of the Monsters, then Gaia beats him out too as I do not recall Yugi ever relying on BLS to take down floatation rings
....unless you want to Count Gaia as an alternate BLS....

I'm very certain, they won't keep him dead. That would be kind of.. fucked up for a childrens show (yeah I know Antinomy but 5D's was different anyway), especially with Ruri still having no clue of anything. But even if he gets the Dragons for a Duel, it will return anyway. you can't really take away Yutos OTK win card.

He never used it "on-screen". Appearently for some fucked up reasons, he had it and DMOC after DM and it's appearently "the ture power of his Deck" or whatever Copycat said...anyway. I think we have different Ace interpretations. To me, it seems like his secret move if he is in a serious situation. Also the Gods are pretty broken themselves, the Tribute part didn't seem to matter that much since he usually splashed them away. I actually think 1 or 2 overpowered bosscards are fitting for MCs. Yusei had Shooting Star and I will ignore anything from Yuma
I was thinking about the Gaia = BLS part but not sure if it's the case in-series. In RL and in Video Games it is, but until we see the next movie I'm not certain if the series will adapt that.

[KingJinzo]

Cool, powerful warriors or warrior-like monsters in armor or have swords.
DM: Black Luster Soldier, Buster Blader, Dark Paladin and Valkyrion.
GX: Bladedge and his fusions.
5D's: Road Warrior.
ZEXAL: Basically every Utopia, and Excalibur.
ARC-V: Enlightment Paladin.

Dragons and dragon-like monsters.
DM: Ra, Slifer/Osiris, Curse of Dragon, Gaia the Dragon Champ, The Winged Dragon #1.
GX: Yubel the Ultimate Terror (not really, but just the thought of it), Five-Headed Dragon (cameo only, never played).
5D's: Stardust, Stardust/Assault, Majestic Star, Shooting Star, Shooting Quasar,
ZEXAL: Leviathan, Numeron, every never-used Number dragon Yuma ever had
ARC-V: Odd-Eyes, Odd-Eyes Pendulum, Odd-Eyes Saber, Odd-Eyes Rebellion, Dark Rebellion, Rune-Eyes, Beast-Eyes

3000 ATK, most often barely used.
DM: Black Luster Soldier
GX: Magma Neos, Chaos Neos, Storm Neos
5D's: Road Warrior, Stardust/Assault
ZEXAL: Utopia Beyond
ARC-V: Odd-Eyes Rebellion, Rune-Eyes, Beast-Eyes (possibly exceptions of barely used, but not used too often either)

2800 ATK that are barely used.
DM: Timaeus, and the other knights might count, too
GX: Marine Neos, Tempest
5D's: Nitro Warrior (8 appearances, 7 OTKs in five duels)
ZEXAL: Utopia Ray Victory (...yeah)
ARC-V: Odd-Eyes Saber

Well, we could go on with almost every other x-ATK, e.g. 2600 ATK (Buster Blader, Bladedge, Wildedge, Plasma Vice, Junk Destroyer, Utopia Ray V, Elephammer), but we got it.

[Hope in the Interstice]

A really impressive list

THat's actually really impressive. Can you think of others in terms of spells and traps?

[KingJinzo]

Monster Reborn, except for Yusei.
Spells that let you draw cards, POT OF GREED, Graceful Charity, Card of Sancity, Mirage of Nightmare, Angel Baton, Gagaga Draw, Shuffle Reborn, etc.
Protective Traps were already mentioned earlier.

[Deadborder]

Honestly most of the protagonists' decks are fairly generic

They follow a vague theme based on the character but usually include a lot of similar "cool" monsters like dragons, warriors, machines, and spellcasters to appeal to kids.

There may be an overarching strategy but a broad one, like Judai's HEROes being about fusing or Yuya using pendulums. Even things like Yusei's deck, which originally seemed to be more defense-oriented, shifts to a more general concept of "whatever" because it's easier for the writer to shove in random quick fixes instead of coming up with victories that follow the original image of the deck or character.

[Dread Kaiser]

Yeah, Hated that
Part 2 Yusei just devolved into "Throw Stardust at it"
Yuma was "Throw ALL of the Utopia" from the start

And even the GX writers couldn't get Neos Contact Fusions off regularly

[Deadborder]

In particular, Zexal ran into duel issues - which I assume is probably in part a result of its setting.

Imagine if Zexal was a standard battle shounen instead of a card game shounen and it makes more sense: "Kid finds magic weapon and must use it to find the other magic weapons, since only a magic weapon can stop another magic weapon."

This lends itself to the usual monster of the week format, fight the thing, get the weapon, etc. And in most cases, this usually means the new weapon of the week will be the most important part.

But what happens when this concept is turned into a card game anime? It means that most of the time, it'll be the main character using their weapon to fight the opponent and their weapon - but this runs directly against the battle system of Yugioh, where you usually attack something to immediately kill it.

So in order to actually show several instances of the monster fights, you have to make up a bunch of stuff to prevent destruction, negate effects, revive the monster,etc.

This all seems to be a logical extension from 5Ds, which had a similar concept of "these monsters are the most important" and had its own share of constantly protecting the ace, especially in the later half of the series.

[Sanokal]

Let's be perfectly honest; the dueling issues started back in GX and continued through 5D's before hitting their peak in ZEXAL.

[Dread Kaiser]

Basically, though 5D's part 1 didn't have much of that issue. but part 2 was even worse then Zexal
Yusei's deck worked as such
Summon Shooting Star, The rest of the deck is cards to keep it alive. Odd as Anime!Shooting Star was nigh indestructable (Quick effect Dodge and its Anti-Destruction effect had unlimited usage)

its always been a rule that important monsters have to be beaten by other monsters (and Death by monster effect has a 50% chance of working)