The low level account cheaters?

I've never bothered to put any of these people to the test the way you did (high marks for that), but yes, the game is FULL of people playing on secondaries. Some of them are, as noted, cheaters banned on another account, but many of them are just using a secondary to fool the matchmaker into letting them play in scrub lobbies. Maybe they cheat, maybe they don't. But they all present like you said, as a new player, but play like they were sweating it out on day one. At this point I can't even remember the last season where I WASN'T noticing a tidal wave of secondaries. It's pretty much a disaster for matchmaking, and this is one example of a problem that, yes, is caused by players, but for which the developer is 100% culpable. Respawn could end secondaries tomorrow but won't because they're the only source of "new players" this game has anymore. Pretty shoddy behavior if you ask me.