You're right about the Playmates figures, but I've always found them to be more whimsy than real serious action figures. They all seem to have a whimsical look about them, and the way their legs articulate is, well, ridiculous.
Personal opinion, of course.
Each film has gotten a few figures, but they're always TOTALLY separate from each other line. Hell, even the Generations figures from Playmates were a little different from their regular line.
Comparing Trek toy licensing to Star Wars (really, ANYTHING to Star Wars), it just doesn't stack up, and that saddens me. But is it the Paramount's/CBS' fault, or is it the fans not purchasing enough for it to be worth it for the toy companies? (You kinda answered that).
I have problems with the articulation and variety--or lack of--of the Diamond Select/Art Asylum figs, and their likenesses aren't perfect--can anyone do a good Shatner?--but I do like them, overall. I wish they'd gone with 6-inch instead of 7-inch, but since I like crossovers, the fact that there are a couple of other companies offering figures from franchises that I really like in that scale, I can work with them.
In the '80s, I loved it when Star Wars and GI Joe figures scaled with each other, though I much preferred the articulation of the Joe figures. Now, it seems that every toy company wants to distinguish their figures by defining a new scale and being the only ones manufacturing in that scale.
Kinda like with model kit categories (rather than individual companies); like tanks? They're one scale. Like airplanes? They're generally in another scale. Cars? Nope, take this other scale.
USS Reliant NCC-1864: 1/537 (or whatever it was) scale. WTF? Couldn't you scale it with the 1/350 Enterprise? They finally made up for it by offering several 1/1000 ships, but come on, this is one that the manufacturer couldn't even offer ships of the same franchise in the same scale.
Sorry, going off-topic.
If I had my way, all figures would either be in the established 3-3/4-inch scale or in 6-inch scale (though I'm changing my mind, to 7-inch (1/10)) with Hasbro-level articulations. Hasbro's articulation is still not perfect, but it works for me.
One thing I will say that I truly appreciate about the Diamond Select Trek figures is that they have a rubber vest over the torso hiding the joint in the mid-section. I'm thinking of stealing that idea. I don't mind joints, but their solution for those that don't seems to be a good one.
If only Paramount and CBS embraced fan productions and replicas as Lucasfilm did (How's Disney?), Trek would have MUCH more influence in the modern world, and MANY more active fans and collectors, in my opinion.