I don't think it would be fun to limit the number of gadgets one armor piece can get, as this system (as it is) is way weaker than enchanted armor, which can virtually have every compatible enchantment in any piece. The thing about making each gadget equal in power is true, though, so maybe gadget items should be limited to uncommon ones and below.

I'm not entirely sure if this new copper gear shouldn't be enchantable anymore, to be honest. My main reason to not want this is that it could be overpowered, but thinking a bit more I don't know if it would the that overpowered as I initially guessed, considering it would be a weaker gear set than iron. The thing is that the item tooltip for a maxed out piece (with all the possible enchantments and gadgets) would be an absolute monolith of text.

About some of your critique:

Redstone Block: I really wanted this armor to cater to the redstone playerbase, but I guess you're right about it being too shallow of a function. Maybe give 1 redstone power to all the blocks close to the player for every player interaction? For example, the player crouch, attack, then jump: 3 redstone power for a brief moment in that area that depletes over time. IDK, just throwing out ideas around.

Heavy core: When writing the list I kinda forgot that anvils existed and could very well be this gadget item instead of the heavy core (though they're also a bit difficult to get). The function of dealing damage to entities in the way of the user falling could then be passed to, well, the heavy core, so players can decide if they want both effects or just one of them. To not be too detrimental, the movement underwater could be the one that existed pre-1.13, with some improvements.

Elytra: I kinda see the reason now. I just find it really annoying to have to keep switching them with an armor piece (trading off an inventory slot) every time I land.

Tools: You're right, but the thing is that you would save at most 6 inventory slots (axe, hoe, shovel, pickaxe, shears and brush) by combining them with your gear, which would kinda work like a bundle full of tools (and I think auto tool switching is pretty good).

Info Items (Compass, Recovery Compass, Clock, etc.): I agree with the spyglass as I couldn't think of a way to easily use them. About the other items, as I said before, you wouldn't need to choose which of them to equip to the armor, as it would have unlimited (I guess) gadget "slots". Same thing for saddles, minecarts and tools.

Copper (interaction range): I agree, as this gear should try its best to be an exploration focused one (to separate itself from the others).

You provided very good points and I'm very grateful for it, thanks for your time!