it's the same way in all versions of the game. buffs stacked passed a soft cap value are logarithmically reduced passed that value.
ATK buffs = 150% soft 300% hard which requires 680%: 2.5 + 0.3*LN(1 + 6.8 - 2.5) = 2.5 + 0.5003 = 3.0003. Anything passed Advance will be significantly reduced in effectiveness.
Breaks = 35% soft (additive) 30% hard (mult) which requires 23%: 0.35 - 1.1*LOG10(1 + 0.35 - 0.23) = 0.35 - 0.0541 = 0.296. Anything passed Breakdown + Full Break will be significantly reduced in effectiveness.
DEF/RES buffs remain mostly unhindered. Prot+Shell+Wall+RED/DEF SB will all still stack fine
And at soft cap, any ability with good multiplier will reach damage cap. So, right now, 150% boost is way more than most actually need.
You wouldn't be stacking attack buffs and using Advance for things like Lifesiphon and Dismissal to begin with. You would be using it for high # of attacks low potency abilities to break the damage cap or for Retaliate. This is where every point of attack counts.