Does anybody catch and train the com mons you encounter toward the beginning of the games? I'm talking about pidgey, bidoof, sentret, wurmple, lillipup, etc. Has anybody challenged the Pokémon League with one of them?
If the Starly line counts, which I doubt because of their competitive presence, then yeah. I always had a Staraptor on my team when I played through Gen 4.
Usually, when HMs were still a thing I'd end up keeping the early route bird in my team for the whole game.
Usually the birds can be pretty useful, however one time I played through White with just Pokémon I could find in the early routes, this was lillipup purrloin pidove munna and pansear, along with a oshawott that never reached its final stage. It was pretty difficult, though the psychic and fire types really helped.
Whenever I start a game, I already decide my full team beforehand. I do catch Pokémon in the early routes but I only use them as fillers while I haven't caught the rest of my team yet. I guess they still get trained to higher levels when I'm using the Exp Share, but I don't really focus on them much.
I used a stoutland too in a playthrough of White. Though I only really used it because I was playing a Nuzlocke... All the same, I was surprised at how useful it was.
I sure have, many times especially pidgeot because I love that one, I've also taken a Rattata to the league way back in Red version. Generally is not uncommon for me to use the early route mons especially if I do a nuzlocke because I don't really have the luxury of a choice there.
I always keep them and use them for when I get better Pokémon but as far as I can remember there are never ones that I fully train since I always work for a certain team in each game and post game I always work for a certain team which I have only achieved in Pokémon Moon so far.
Pidgeot, Furret, Swellow, Luxray and Staraptor, Liepard, Talonflame. I think I used an Early route Pokémon for most of my playthroughs at one point in time.
By Route 2 in Pokémon Sun, I already had a Magnemite, Slowpoke, and Drifloon on my team. They helped me to beat the League. I would call them early.
I think it just depended on who they were and how much I liked them lol. I think I always kept Pikachu, Plusle, Minun, and maybe Skitty. And of course there was always that one Pokémon who became the HM decoy with the weaker moves like Cut, Flash, etc.
I had Starly and Shinx when I had Platinum and Fletchling in Y. And lemme tell y'all something. STARAPTOR WAS A BOSS.
I highly doubt this counts. But I kept Gawaine the Vikavolt for most of Sun, although I replaced her with Nebby the Solgaleo for the League. In ORAS, I had a Zigzagoon called Bandit that ended up at Level 84 last time I checked. I was going to use him as my HM slave, but he became useful for weakening 'Mons so I kept him around. #MissingNo
I had a grubbin for a while, but it was slower than the rest of my party so I replaced it. A level 84 linoone sounds awesome.
For some reason, in Sun every 'Mon I caught myself had god-awful Speed. I tried everything and eventually they became faster, but it was a long, hard slog. It is awesome! I tried taking on the Battle Resort with him and got pretty far in Triple Battles. #MissingNo
For the most part, I do keep one or two "Early Routers" on my team. The birds in prior gens, especially, due to Fly. Unfortunately I never had the experience of using Staraptor on my main team, so when a gen IV remake happens, you'll know who is on my team!
I have to agree about using the regional bird for the HM, but now that's not needed I really doubt I'll use them alll the way through. In SuMo I've used the regional a little bit but only because I like grinding up everything a bit at the start, once I can catch it's evolved form in the wild and have the livedex spot filled I won't be using it.