The way I see it, there are four broad categories of Lego Themes
-Abstract-Based: stuff like Creator, X-Pods, (Anyone else remember the X-Pods? Me neither) Mixels, Racers, Mindstorms, and (arguably) City, (before it turned more into "police" with some occasional other buildings) where the main aim is to promote creativity and building within as minimal a framework as possible. It isn't quite the same as the classic bucket-o-bricks, as there's at least a vague overall idea and a specific color palette you have to work within, but it's still very very broad. And while it does feel like this has receded into the background a little too much sometimes, it's still there, still around. I may not buy it myself very often, but I appreciate what it does, and I do think it's still pretty popular among kids?
-Premise-Based: As mentioned above, this is the stuff sitting in the middle ground, stuff like Exo-Force, Adventurers, Spybotics, Friends, Atlantis, Life on Mars/Mars Mission, Ultra Agents, and many many many more besides, since the early to mid 90s. It's not got a super in-depth narrative, but it has a handful of faction-based sets and an overall broad idea that serves as a framework for kids to do whatever they please with. Aside from Ultra Agents and a couple others like it, these seem to have dropped off as of late. Personally I think they worked best when there was more variety among them, so there'd be a little something for everyone, even those not necessarily interested in the mundanity of the abstract sets or the deeplore of the heavily Story-based ones. Personally there are a couple of Premises (CoughExoForceCough, CoughSpyboticsCough) that I feel could have been better served had they been fleshed out in greater detail and given a full Story treatment, but overall I think the value of these kinds as a middle ground between the story-driven and the abstract is massively underappreciated.
-Story-Based; which I guiltily admit is what I personally lean toward the most. Bionicle and Ninjago are of course the standout examples, but HF, Chima and Nexo Knights also count in this category, of course, and arguably the new Lego Movie tie-ins as well. Bionicle had a book series, movies, and a ton of other stuff besides. Ninjago, HF, Chima, and Nexo Knights all had shows, actually televised on a major cartoon broadcasting network. The Lego Movie is, well, you know. Point is, these are things created by Lego themselves, but which have official story media taking arguably as much of an important role as the sets they're meant to promote, and depending on the execution, can develop into something pretty lore-dense, detailed, and most important - emotionally investing. Three of the five have of course fallen short of the mark, but for all their problems I do feel HF and Nexo Knights had the potential there. (Chima I'm more iffy on, but still.) I don't know as much about Elves, but it may also be in this category? Idunno.
The question of the hour is whether or not this stifles creativity in kids. Personally, my answer would be no, as long as the Abstract and Premise-type themes are still running just as strong in parallel. If everything was only story themes, then yeah, maybe it would get to be a bit too much. But given all the MOCs and things Bionicle alone generated, I feel that ultimately, even a heavy story such as that one isn't as reductive to creativity as one would assume at first glance. And honestly, most kids aren't concerned with keeping 110% in-line with canon anyway, so it's kind of a moot point. As a kid, I made a red-and-green Rahkshi Of Christmas that shot strings of christmas lights from its staff to tie up the Toa, fully aware that something like that could never actually show up in the official story. Did I care? Heck naw.
-The fourth category is of course Liscense-based themes. When it comes down to it, they're not that different from story/premise based stuff, with the main distinctions being that the story is generated from outside Lego, Lego has to pay that source royalties and stuff, (often inflating the price of the sets as an unfortunate side-effect, the so-called "Star Wars Tax") and most if not all of the designs for the sets are based off of pre-existing content or ideas, which can be limiting in some ways but also force creativity on the part of the designers, in attempting to maintain accuracy to the source. As far as how these minute differences impact the issue, I feel that it's honestly no more or less damaging to creativity than the Lego-original story-based themes, and I do like licensed themes as a chance to see a Lego adaptation of material I already like. (Honestly, in another timeline where this would be possible, I would be all over a non-Kreo Transformers line.)
At the same time, in terms of actual business effects on Lego, I see Licensed themes as something like a perscription drug; in small doses it can actually improve the company's performance and fame, but if they become over-reliant on them it could get very dangerous and leave them in permanent debt to other entertainment giants. (CoughMouseCough) Plus, on a purely subjective note, I'm just kind of sick of Star Wars steamrolling everything else in the Lego section, even though I enjoy the new movies. So while I don't hate Licensed themes, I do think they're something best kept in check and smaller in proportion than the other three categories. I'm not opposed to them existing, just nervous about how much Lego seems to be leaning on them in recent years.
-So basically, my view is that Lego needs to downplay the Licensed themes, push the Abstract stuff more than they have been as of late, and try to diversify the Premise-based stuff back to the wide ranges of ideas we saw in the mid-2000s. The Story-Based themes should remain a small but important niche, Ninjago (or whatever may succeed it as it succeeded Bionicle) running alongside one or two other experimental lines like Chima or Nexo Knights, and maybe a constraction thing as well again, if santa decides we've been particularly good this year.
That's my two cents, anyway.