the content issue isn't even a difficulty or number of monster related
it's a global pacing issue
it's tied to wound system that make every monster a piñata that dies too fast and give too much rewards, people just steamroll the game to the end and don't actually progress like they used to
and adding an rng grind with the same monster but harder won't change that
worse that that it's too late to fix now that people are already at the end
it's game design 101 and would have been spotted instantly with any level of actual playtesting
and that's just a single issue among others
tl;dr capcom is incompetent on more levels than you can think off