No. Not always. Over here it's entirely possible to use a Guardian vigor grid + specific builds (i.e. Perseus' total shutdown build, i.e.2 Yorimitsu triple FB + couple rounds of NAtk during peak hour, where your frontloading dmg is so high the boss is dead before anyone else can finish their rotation) to outdmg decent 100% users. I've lost to a guy on my FL with nearly 10k less Atk power than my team does quite a few times. It all depends on team + weapon skills + real time control.
.... obviously this doesn't apply to space whales with 90~100k power grids but then they prolly wouldn't even use 100% and might just use Burst Streak summons instead...