Sure. You are correct that the Artificer went through less hurdles than psionics, but most people had a pretty solid idea of sort of Artificer they wanted: an Eberron-style. The first draft was a wizard one, but that was unpopular. Psionics went through four editions of various design iterations and were less defined by a particular setting in terms of their flavor. But the point is not how many passes one class went through versus the other - that's just moving goal posts - the point is that the Artificer is similarly niche like psionics, but also one of the most popularly requested additions to the game, much like how the Artificer was.Ok, let's compare the artificer shall we?
And, we're not going to get WotC psionic rules until such time as a majority of people are on board with the rules, just like anything else they've added to the game. That magic 70% number that I've seen floated around a few times. Do YOU think they've reached that threshold with the current psionic rules?
Hugely popular? Difficult to prove one way or another. However, is it sufficiently popular to warrant official publication in 5e? Sure. It has been popular enough to repeatedly show up in 4 editions, which is four times more than the Warlord can say. We can also say that psionics are popular enough that WotC is still trying to bring psionics back instead of dropping it like they have so many other concepts. Or how many versions of psionics exists on the DMs Guild? How many homebrew versions of psionics are out there? It's not exactly as if psionics are on the same degree of niche as some sort of anime princess maid class. It's something that has popped up in all past editions of D&D that has gotten people to continue writing and advocating for.Show me where psionics is this hugely popular thing. I'm more than willing to admit I'm wrong. But, so far, all people can do is play dueling anecdotes about their home game. Which, well, doesn't prove anything. What evidence do you have that psionics aren't languishing in the same development Hell as rangers?
* Also the development hell of rangers probably has a lot to do with how WotC doesn't want to invalidate customer's PHBs. Not sure how psionics is comparable in that regard apart from taking a lot of rehashing behind closed doors.