I think that the matter is not that RS3 doesn't progress, it's that they've basically broken player progression so interesting training systems don't matter.

Partly the issue is also possibly that RS3 simply does not quite take ideas far enough to make them something amazing. Think Shattered Worlds - folks were excited about it but it only fell short of OSRS gold becoming something really wonderful. Subsequently Jagex just kinda goes to the next thing, which is also frequently half-baked. It's mostly trash mobs. It could have been really exciting if we got lots of new, exciting, powerful monsters to combat but instead we got dull crap. Like it was this close though,y'understand?

And I believe OSRS has lower standards for what's an exciting update anyhow, many players are only doing their thing and if they don't get updates for a little while it isn't a huge deal since they mean to grind for hundreds of hours doing exactly the same thing and they're happy to do that. Should they get some new way to spend countless hours every once in a while it is a welcomed thing. On RS3 although it's rather like... Eh. 99s are really easy, so if a new training procedure isn't super good money and/or AFK what is even the point to most people? Similar story with items, OSRS players actually have a reasonable desire for lower grade weaponry because individuals aren't all level 99 within their battle stats so it's easy to add things that have a greater effect. Not to mention PVP is something, so some random bizarre weapon can become the focal point of an entire account.

There is also a perception of RS3 not having many updates, but it will get some fairly massive updates and if it will capture those massive updates it introduces a whole lot of things. Idk, there is so many factors at play and it's hardly"RS3 doesn't progress." And it's a sizable piece of skilling content comparable to Shifting Tombs, it probably is really larger and much more interesting than Tombs as well.

Upping slayer into 120 even with what is there now still feels bland and Old School RS Gold lacking in material. Dead content structure and watertodt, really nice indeed lul.