RNG is one of those strange subjects in MMO's, where every time it comes up you'll have a crowd of players who defend it to the death despite not really having a reason why. Usually the arguments are "it's fine", "it could be worse", "you want everything on a plate!", "it's necessary somehow", "it makes rare things rare!" and so on. While a little RNG is staple in gaming, I don't think players even know why they argue for heavy RNG, it's just become ingrained so deeply into gaming they assume it's somehow for the best.
Pentamelding itself is a mess. It's a system in place to burn the thousands of materia that pour into the economy because they've made materia so easy to get. But they don't want to force everyone to use the system, so they make it largely redundant. Since the system is redundant and materia is easier than ever to get, the whole thing hardly works and materia is worthless after the start of a patch. Materia 9 being "worse" than 8's just confuses newer players too. At this point they might as well scrap it.
But no, we'll never see a rework because we're so focused on how the RNG is "fine" because pentamelds are a waste and materia is dirt cheap.
I'd also be happy to see things like EX mounts being available for totems at release, 1 piece of class loot in level cap dungeons, Bozja notes for a high coin cost, instance TT cards available from NPC's and so on. Grind is fine when there's a clear goal. I'd be digging into that content right now if changes like that existed, instead of ignoring them because I can get the reward with Echo or life is too short to potentially waste 100 hours on something that drops in 5 hours average.
You don't. There are no Expert Recipes announced yet and the next combat set isn't until 6.2. The new DoH/DoL set will be mostly worthless for several months. You're better off running maps for an hour and buying the set dirt cheap with gil a few weeks into the patch.