These descriptions are pretty accurate, but obviously these will vary slightly with different people. Most people I know when they start off only use characters they like and try to stick with them. I personally used Kirby at first because I liked him the most, and I stuck with him most of the time. The OP thinks people choose their character based on their "superior" moveset (they think Kirby's fsmash is godly or something simple like that), which is somewhat true. What eventually steered me away from Kirby at the time was that he was very light and died easily, I experimented with Captain Falcon and Samus but I dropped them because I thought they had a bad roll, which was at the time a big part of my defensive game, and because their recoveries sucked especially compared to Kirby. I picked up Ness after deciding he had a good roll, an excellent recovery with his dj and pk thunder (my friends and I did very basic edgeguarding, so I didn't know he had a terrible recovery and thought it was only about distance). Even now at my level I stick with Ness because he is now my favorite character of the roster and haven't gone back to maining Kirby because he is better than Ness.
I'm at 5a right now definately, I am learning to use advanced techniques and combos very consistantly, I can do them like 75% of the time. I am also experimenting and discovering more combos I can use, for example I am currently experimenting with the walls on Hyrule for excellent combos/killers. It will be a long while before I get to 5b since I don't have online ssb working atm and there are very few ssb64 players who I only see once a month at Brawl tournaments where I bring my N64 and play ssb64 on a free setup. And of these people I play, about 99% of them are well below my level that I end up 4 or 5 stocking. I have played two good people who were around my level so far of the dozens of people I played over the course of months. I found I learn best playing people at or above my level, which unfortunately are hard to find offline.