take punishing losses against progressively more skilled players

how do you make sure that the enemies they face are progressively better?

You don't. There is no perfect ladder of progression of opponents. Sometimes you'll have easy wins, sometimes it'll be competitive and sometimes you get rekt. That's life. I'm not suggesting anyone attempt to do what you're describing and SBMM doesn't accomplish that stated goal either.

My phrase quoted above doesn't mean "we should choreograph a ladder of progression that makes every game incrementally enjoyable for new players."

It means, a new player will start off getting slapped to death in most of their games. Then they'll start improving and noticing what you're doing wrong (while building a foundational level of comfort with the game controls/mechanics).

They'll progress from only being competitive against fellow noobs, to being competitive against bad players, then average players then if you put in the work and show the aptitude they'll actually get good at the game.

tossing new players to the wolves will cause them to leave the game much faster

I literally could not care less about someone who's bad at something wanting to feel the reward of performing well without putting in the work to achieve that reward.

If you're picking up a COD for the first time day one at MW 2019's launch and you expect to do well, you're delusional. If you don't expect brand new players to have to grind out the intro suck to get good, I don't understand you. Not you directly, "you" meaning any of the many many people who share this SBMM support mindset. It's a game, play it. Learn it. Improve.

I thought "every gets a trophy" shticks were a tongue in cheek exaggeration but people today truly are terrified of just being shitty at something until you learn enough to be competent. A worldwide matchmaking system shouldn't be predicated on massaging the ego of the lowest common denominators among the player base.