Here's my vid. Sorry about the bad sound quality and the lighting -- I didn't have time this week to shoot this at our studio.
I'm not a rumba master, nor do I claim to be.This vid reflects my best understanding after years of study with a series of Cuban pros (including a year spent studying at ISA) and social dancing in Cuba.
Very nice video
However, you're not doing the mollello in your dance demo.

If you look at your guaguanco demo from 4:05 -- when you really get into it

-- what you call "small mollello" is really the action produced by raising your heels off the ground, which is exactly the action we see in good rumberos (and YM's vids) So great job with that.

It is that raising of the heels action that is creating the nice springy effect (as you call it, the folkloric look). Whereas a
mollello would mean that your head is lowering and rising along with the rest of your body as your knees bend because your whole body is going down then back up, with your heels down (no matter how small the lowering is, your head still goes down if you're doing a mollello--you can see it when you demo mollellos earlier in the video). But if your knees bend because you are
raising your heels rather than because you are
lowering your body (which would be the mollello), and your head remains level while your heels go up, that is a very different action from a mollello and is exactly the action that I see used by the good rumberos. (So again, awesome job with your rumba

) The difference between that raised heel action and a "small mollello" is subtle but it makes the difference between nice rumba movement and an "ok" version, so I think that if we are discussing the mollello we need to be clear about and acknowledge this distinction.
I suppose the mollello is a way to teach beginners how to "fake" that action. Whether it is indeed the best teaching method, I'm not sure. For me personally, if anything it made whatever rumba movement I already had worse. So it makes me think: what if rumba beginners were taught directly how to step, without mollello, and as they get more advanced, how to use the heel raising action, smaller at first of course, like the experienced rumberos do?
Another observation: I keep pointing out the female dancers and it's because the basic rumba movement is the same in men and women, except of course men's is sharper and with more accented upper body movement and accents whereas women's is softer and with more accented hip movement. I think it is the men's sharper movement and somewhat stronger raised heel/springy knees action that is confusing this whole issue of the mollello (in light of the distinction I highlighted above). But if you look at the female dancers, it becomes very clear that there is no down-and-up mollello action anywhere in their dancing.
So the next, obvious question is: is men's basic rumba stepping action so different from women's that it requires a mollello whereas women's movement does not? To me the answer is no. Also, men and women are generally taught to step the same way in beginner rumba classes, and it is usually with the mollelloed sideways-and-back basic, as I was taught as well.