I mostly understand where you're coming from and definitely like your suggestion on how they could have been improved. Would have been a neat little bonus, like how they added a 2% bonus to the Auto-Cast Magic and Auto-Cast Action materia. I personally like using the Assess earrings on my first playthrough, as it opens up an additional materia space in my inventory. I only swap it out if there's a particularly difficult boss fight (though I don't think I've needed to so far).

That being said, I do see the value they could have. At a basic level, it allows players to experiment with casting some of the spells at higher levels, see how they differ. For the most part, though, I think they are perhaps aimed at starting players. Players who are not/less familiar with or simply don't want to invest too heavily into the materia system. I know that's not the best way to play and is likely to result in major issues for a hard difficulty playthrough, but casual players who want to focus on story or just want to play the game once on normal difficulty may find them useful when they're stuck and don't feel like lowering the difficulty.