I don't agree with the basic premise.
Sure, some things are annoying to be variable, but we wouldn't have them at all if they weren't. Other things NEED to be variable. The OP mentions modifiers to spellcasting for vigorous or violent motion. The only way to make that non-variable would be to apply it all the time or none of the time. Since there needs to be some drawback for that, it can't be none of the time.
A barbarian raging - again, it's nto going to be there allt eh time, so the only "non-variable" modifier for it is none of the time.
I'm not trying to be simulationist, but some things make a lot of sense as variable.
Now, that doesn't mean I wouldn't like to reduce some of the variables - moving power attack to a few set points instead of the entire range would reduce the options to allow precalculating. But finding a sweet spot that works for high and low level characters isn't the easiest thing.
Look, if you can have buffs/debuffs from spells and other effects and accept it, then you need to be able to accept that other things also need to only be in affect some time.
Well, you don't NEED to.

Your DM can do anything they want. That might be a good chance for you to step up to the DM screen and come up with house rules. Give it a try. It might streamline it exactly as you think and be a lot of fun for you and your players.
Cheers,
=Blue(23)