@ReadyButNot, well, it's a rough draft, of course. Your points are pretty good.
Basically, I was thinking that if you'd almost need two sets of rules here: one for an all-Tiny game and one for a regular game that also has TIny PCs. So it makes sense that in an all-Tiny game, Tiny creatures would have what would be, to them, heavy weapons.
It would probably make a lot more sense if o5e/LU had kept weapon sizes like they had back in 3e. Sadly, it didn't, and considering that neither 05e nor LU nickle-and-dime creatures with +2 bonuses or -2 penalties anymore, and disadvantages is kind of an all-or-nothing deal, I'm not sure what, exactly I could to do to represent not being able to use a too-large weapon.
Except... perhaps if a weapon is two size categories too big, you can't use proficiency with it. So a foot-tall pixie could use a longsword built for a medium creature, but they'd use straight Strength with it, not Str + PB. I dunno; I need to think about it a bit.
A good point about the mechanical weapons, although D&D has never really cared about draw weight. Even LU only has one type of compound bow, IIRC.
Adding the full Strength is a bit odd, I agree, but again, I was thinking about an all-Tiny game.
So yeah, rough draft thing. Thanks for your input!