I agree about grenades, but not your reasoning for them. Any 'grenade overwatch' alien is going to run out of grenades pretty quick, and in any case vanilla AI doesn't like to throw grenades at single soldiers, so just not clumping up avoids a most of it.
Vanilla AI is also not going to cooperate too well with staying put in some tower or somesuch, unless physically prevented from leaving.
Aliens are
meant to be powerful. Us Earthlings are the underdogs in this fight, after all.
Reaction-fire rockets can be avoided in various ways. But sometimes you
want the reaction rocket, so turning this off completely is a no-go. Not aware of any mod that does this specifically.
Rotating the soldier and depleting TU before hitting 'end turn' are the most easily accessible solution. Giving the soldier a sidearm and marking this as the preferred reaction weapon works, too. Disabling snap shot, or converting it into, say, auto-shot via a ruleset change.
Also, immersion-wise, if I'm an Earth Defence Force redshirt with a big missile launcher and suddenly see a Chryssalid pop up in a cluster of my comrades, you can bet on me taking the shot instead of following some asinine 'no friendly fire' rule.
In any case, making your own mod is the easiest solution to the above problems. You can tweak things to be exactly as you like, no-one can tell you to take these changes you like and also those you don't want as a package. OXC(E) is very easy to mod, and if you have trouble, you can always ask for help here.