The setups for physical characters become solved:
Elemental/Added Effect/Counter-Stacking/Deathblow(Or Morph/w Ancient Weapon)+Added Cut;
The limited availability of most of the listed materia makes it pretty difficult to deck out your whole cast, too.
Furthermore, physical characters especially could benefit from triple or quadruple-linked materia slots, allowing, for example, one Deathblow to be linked with Added Cut and HP Absorb or Command Counter. Those multi-linked slots could be exclusive to weapons found on physical-based characters(Cid, Tifa).
I think these are interesting points. I try to make my characters as unique as possible, but if you are going for variety in melee characters, they mostly come down to everything feeling very samey for most of the game.
Once you get deatblow+added cut, that helps separate the physical attacker in your party, the damage output really becomes ridiculous, especially when paired with elemental.
But thats really only one option that differentiates them, and it's quite late into the game.
I've thought about the benefits you would get from adding multi-cut, or slash all earlier. But, they both seem imbalanced to include earlier. Enemies would have to be greatly beefed up imo, to compensate for the additional damage up. Also, weapons like enemy launcher that hit all opponents would suffer a little if you had access to slash all.
Another point would be, to even be capable of doing things like mp/hp absorb to be used with physical skills, you'd need multiple copies of death blow. And you get that pretty late, and you aren't gonna master it for a very long time. By the time it happens, it'll basically be irrelevant. And even still, it's like, 10% hp gain? It feels next to worthless for two copies of deathblow, which you won't even have access to.
I think what I'd like to see is another true offensive melee type of materia earlier in the game. Maybe a new one entirely?
you have added cut + death blow for 3x total damage (can pair with hp/mp with multiple copies)
2x cut for 2x damage (can't pair with anything)
4x cut for 4x damage (can't pair)
slash all for 1x damage vs all (can't pair)
Deatblow is interesting because you can pair it, but for all the others listed, you can't. What would be cool would be an in-between that could link, that isn't as powerful as deathblow or 2x cut, but would effectively work with support materia. Let's say just for example something like "insert name here" 1.5x attack, paired with added cut, and a second copy paired with hp absorb, for a 2.5x damage attack, that could be really fun, but if you got it too early it'd have the same imbalance issues as getting 2x cut too early. And if you get it too late, it'd lose most of its use, unless an additional rank was added to power it up (but that would have to taken insane AP, so you couldnt get it until the same time as 4x cut)
Maybe a less complex addition could be Darkside, sacrifice 30% hp, to deal 2x damage, something like that, on your tank characters.
Just ideas, I dunno, I do think it's a waste that most interesting attack command materia only comes late game, cause you lose that variety for 75% of the game. It's also a problem that things like hp absorb require 2x of the paired materia to be worth it (cause you wanna use added cut always), and also the HP restore thingy is only 10%, making it feel worthless anyways.
general, the fact that most good command attack materia can't be paired, and for it to be worthwhile, you need multiple pairs, makes it feel a whole lot less interesting than it could be, and I do think thats a shame in general, but it's really the fault of the base game.
I think some cool things could be done to fix that, but it would be a lot of work, potentially create balance issues, and probably you would have to throw away other skills to make way for new ones (morph

?)