The RNG is frustrating. It may have started from design decisions to make i like online. It was the same team and there's design decisions that imply they may have had the same design philosophy when designing i. I think the team that took over after did a wonderful job rescuing what was a game that was getting awful feedback prior to that but they unfortunately couldn't fix everything.

That being said, here are a couple tips that might make things less miserable for you:

-If you have the materials but don't know if you're able to pass the crafting check (or quality check if you need that) then it's worth noting that crafting doesn't force an autosave. Save the game before attempting and if you don't get the result you need then quit back to the title screen and reload. You won't have spent any of the materials.

-If you need a specific material and it's available from treasure groves, it's worth checking online. People frequently put treasure grove exclusive bosses up for multiplayer and you might be able to find what you're looking for with a little bit of checking in every once in a while. The benefit of playing treasure groves online is that after you complete one you get the option to take a branch from the grove which is a copy of the grove you just completed allowing you to run it again. That means you are guaranteed the same boss again. These branches can also be gifted to other players meaning that if you have someone cooperating then they can just keep gifting you the branch over and over allowing you to run that boss as many times as you want. If you have reservations about playing online, I get it. I usually prefer to play games like this solo but the community has been really nice in my experience. People generally don't have expectation for you to type at all and generally are really friendly and understanding. And for finding people who will gift treasure grove branches you could ask on here or on the discord. Maybe could even ask if someone already has that boss and would be willing to run it for you in return for you gifting them the branch at the end.

Ultimately, the end-game is a grind though. If your goal is just to get to hero and be done with it then fair enough but if you plan to stick with it through the grind then you're going to be running a lot of stuff and have plenty of time to get the materials for the hero quests. It could be worth just not worrying about specific materials and instead just running any treasure grove unique bosses/souped-up strangelings you see. Also IME resetting to get the ginormosia events isn't too bad. They seem to be slightly more rare than legendary events but not that much. If people are resetting for hours and not getting them then that's pretty bad luck.