I don't play 451v, but that pass completion is lower than what I achieve.
If using long or mixed passing my AM compliments passing between 83-86% and mixed/short is often 87-89 with my maximum about 91.i think I saw opponent with 93 completion rate. Again, not using that formation, rather one with 4 midfielders.

I'm sure it depends on both teams, player skill, tackling style and others. I will say it's clear one rate is not ideal across all formations