Uh yeah looks like the point is moot then, scrap that team. I will say that this seems like it may have nerfed Firefly TOO much; the delayed revival is pretty brutal already. Back to the drawing board. Though... from the phrasing, it sounds like FFT Monk's Hamedo still works (65% of the time, melee only), since it cancels the enemy attack rather than reduces damage? Just want to confirm / deny that.
If a team's only argument to beat floor 3 in a team with Aika heavily relied on Delta Shield, I don't think the issue lies within Aika, but within the team.
Huh? This I'd dramatically disagree with. The Dungeon is built around teamwork; rather obviously, if you disable one cog in the engine, the whole thing can fall apart. The price of not being able to magically heal your team is pretty strong; presumably you're using inefficient item heals to get around it. If you're accepting this inefficiency but not getting anything in return, then your team will fail. It'd be like saying that if Cloud lost his materia and the team lost as a result, then the problem was with the team. Tonfa's team had Cover-Cloud as a main part of its strategy, and thus Aika's poor physical durability wasn't a big problem; take that away and the team would be really awful. But this is silly because he DID have Cover, from Floor 1 even, and he relied on it heavily to beat a ton of Floors. Nothing wrong with that.
This is in fact the exact reason I said Chris wouldn't cut it- she gets Silent Lake way too late (same problem with Beecham). If you're building a team to abuse Silent Lake / magic voiding (or any gimmick), but it doesn't have access to said gimmick for a long while, then there's a really good likelihood the team will wipe before it ever gets to play with its shiny toys.
(EDIT: If you "disable one engine in the cog?" That's one hell of a cog if it's made of multiple engines.)