Two Sets of Rules, the Good and Bad?

[Sorinth]

It's absolutely bizarre that an Empyrean fighting a dragon attacks less often than an Empyrean fighting a dragon and two zombies, purely because of Legendary Actions. That degrades verisimilitude.

Doesn't the same apply to opportunity attacks? Why does a character get more attacks when fighting against a target that is constantly moving in/out of it's threat range?

Or how about GWM. If killing a creature is supposed to provide some sort of "morale" boost that allows for an extra attack, why wouldn't the Empyrean being outnumbered not also give them a "morale" extra attack(s).