I think RWBY making this far is indicative of 1. just how popular RWBY was, and 2. RoosterTeeth's lack of options.
RWBY became popular in the first place because it existed in a near vacuum. It was the only cool Western animation at the time that had appeal to teenagers and up. Everything else was crude humor sitcoms or boring Saturday morning cartoons. There was ATLA but that had ended years before and the sequel was unpopular. Anime was just starting to become mainstream because of streaming but it hadn't solidified yet. So RWBY won by default. For a lot of people, it was the only option they were aware of. RoosterTeeth also had a cult following because of Red vs Blue which helped spread word of mouth. So RWBY built up a big fanbase, big enough that a decade later even a fraction of the remaining fans still interested in RWBY is still a sizeable number.
As for RoosterTeeth, RT doesn't exist in a thriving animation industry like anime production companies do. In Japan, anime companies can pick and choose what projects they want to work on. There are so many shows in production that companies can be booked years in advance. RoosterTeeth has no luxury. Working on RWBY and their other in house projects are the only real options they have, unless they want to start doing 3D CGI for television commercials. RoosterTeeth's other new show, GenLock, didn't take off like RWBY did. It didn't have the charm, and came later than RWBY, after anime had become entrenched in the zeitgeist and people are aware that they if they want to watch cool animated shows, they aren't forced to settle for GenLock. There are thousands of anime out there at their fingertips that they might derive more enjoyment from. So RT continues to focus on RWBY. It's what they've got.
Honestly, RWBY would be pretty… not simple, but not exactly hard to fix. If Rooster Teeth was willing to suffer through the pain of what it would take to do so.
1. It desperately needs a reboot. The show feels almost aimless at times, and there is just to damned much going on that I think they’re having issues focusing on the overall plot.
Jettison the gods plot point for one. Jettison Oz’s immortality while we’re at it. Salem can stick around, though I think she’d work better without the immortality.
Have her be a last remnant, hehehe, of Mantle or Mistral’s old aristocratic class before the Great War. Make it a shadow war between her and Oz, who you could give a connection to the last king of Vale (descendant or distant relation), with the Grimm as a threat ever looming in the background.
Or I don’t know, have her be a Faunus and slot her in to Sienna Khan’s place. I’m just spitballing here.
2. Despite what I say above RWBY also has the problem of feeling very rushed at times. It goes from dead air to sudden breakneck runaway train with very little in between. The pacing is absolutely fucked at this stage.
I feel like this could be fixed with either longer episodes or longer seasons. Preferably both. This gives time for the characters to breathe and be better established by expanding on backstory or giving them some actual screen time.
3. Cut the cast down. There are so many characters in rwby that it can actually get rather confusing at times. Rooster Teeth need to sit their asses down with a competent editor and writing staff and start asking themselves if certain characters are at all necessary.
Sienna Khan, Hazel, Whitely and Willow, Robin and her merry band, the Ace corps. Hell, Ren and Nora barely did anything in the last couple of seasons, and Oscar could be put on the chopping block by getting rid of the Oz immortality angle.
4. Make at least some of your villains actually compelling in some way. None of the villains are at all interesting.
Tyrian is a psychopath, Cinder is a power hungry lunatic, no one has any idea what Salem actually wants, Watts has more going on than all of the above but his jealousy is ultimately uninteresting, Hazel is an actual idiot, Adam went from semi interesting leader of a racial revolution group to an abusive boyfriend and genocide advocate, and Mercury and Emerald haven’t really mattered since season three.
Most importantly, we don’t see the backstory of most of these characters. We get told a lot, but we don’t see a lot.
I’m sure there’s more, but I’m working on my phone here and these are my four main complaints. Most of the rest of it is honestly nitpicking.