I'm positive that the only reason they're 'against' mods is because of the huge console install base in Glorious Nippon and they want to avoid perceptions of 'unfair advantages.' Yoshi-P is an old school MMO gamer, so he knows the value and almost assuredly used some himself.
P7S is a good example of this too. And the fallout that happened.
There's a mechanic called "Inviolate Purgation" a little over halfway into the fight. The intended way to solve it seemed to be to use south platform for stacks and north platforms for spreads. But that made healing awkward and forced melee downtime. People found on week 1 though that you could fit the stacks and the spreads on one platform, and if you had the stacks at the back of the platform, you wouldn't cover the other one.
This basically became the defacto method because it was way easier, allowed much easier healing, and meant melee could maintain 100% uptime. But the positioning was very precise. And because of how the arena is designed, you couldn't put down the waymarks without modding (or saving a modded set of waymarks).
NA/EU didn't give a shit. And it didn't cause much of a fuss even among console players cause you didn't need to have mods to save it. You could just grab it from someone else as you would do with any other set of markers. JP were pissed though, and if you put down the markers then they would consider it "illegitimate" and either kick you, leave the party, or outright disband. This led to a "naughty modders" statement and then they changed the arena to be bigger after clearing the fight so you can put down the markers.
Personally. I think the bigger issue is that P7S was a shit fight. I genuinely think that it's the worst savage they've ever made since Alte Roite back in O1S. Nothing hard happened until the boss was at like 20%. With current gear score, you reliably skip the only hard bit.