We can probably assume that someone like Luffy has a stronger soul than someone like Nami as an example, but that doesn't really tell us much because there aren't any noteworthy soul resistance feats to scale either of them from.
I think weaker characters than Grimmjow are easily RCing Doflamingo. I don't even get the Doflamingo wank here, he's barely even a high tier in his own verse, below practically every commander, why are we entertaining him going up against one of Bleach's strongest top tiers.
If they made a crossover they'd probably ignore every established rule just for simplicity and for the sake of writing, they've already done this with the Toriko/Dragon Ball/One Piece crossovers. But we aren't discussing a fight between hypothetical crossover characters, we're discussing a fight between the characters as they are from their respective verses.
Luffy’s soul is not on the same level as a background character’s soul — not even close, actually. I only brought this up because someone a few posts earlier tried to imply that One Piece characters are just regular humans with common, fodder-level souls, when they clearly aren’t.
Imu’s soul is not the same as Don Gringo’s soul, not even close — infinitely different.
But then we also have to look at feats. Doflamingo is far more impressive than Grimmjow. This isn't the case in One Piece because it has energy systems, but a verse like One Punch Man can only be debated by feats, since it doesn’t have spiritual energy, only physical energy. Looking at feats is always useful.
In the One Piece/Toriko/DBZ crossover, not only were the energies equalized, but the characters themselves were treated as equalized as well. Energy equalized or not, a single Kamehameha would turn Luffy into dust, and Toriko is multi-planetary too
[automerge]1763921316[/automerge]
Bleach characters aren't normal people either. Even if we equalize it, Aizen negates everything Doffy has by this logic with his "haki" being so much stronger.
Besides, OP needs better soul resistance to even compete. Characters who are made up of hundreds of thousands of souls are affected by Aizen.
But then we run into the dilemma of ‘how do you quantify energy from different universes?’
The only thing left is to compare power feats
And Bleach isn’t that much superior to One Piece in on-screen feats