I hate to say it, but I'm to the point where I think haste should simply be removed from the game entirely. Potions of haste and the spell. Anything that gives haste. It's way too much.
Alternatively, the 5e rules for haste could be applied. They allow for only one attack on the extra action (even for classes with double attack) and only one non-cantrip spell per turn no matter what.
