RNG is a staple in most games because it is a damn easy way to force replayability. Go through a dungeon have a chance to get an item, yadda yadda. Fine, not to huge, but....RNG on crafting to a point where you could fail 100 times is too much.

I am talking about pentamelding. It is a bit out of hand, and really feels punitive. I get that it is totally optional and all that but it feels tuned wrong.

I would suggest an opposite version of RNG for things like this. Have an RNG chance, that is quite low of getting it early, and then just tell us how many materia it takes to put it on there. So say first slot top tier materia, costs 15, but you have a 5% chance of getting it instantly with every attempt. Just something to make it not feel like a bottomless pit of screw you.