A little detail that slipped mention is the fact that later plate armor were made to resist bullets and that fire arms and melee weapons co-existed for quite a long time on the battle field. With a dynamics between better firearms, worsening armor economics and ergonomics as an equation.

As seen on modern EOD technicians vs infantry there's clearly still ergo-economics at play on how to armor combatants.

I'm not sure I would say armor is fully solved yet