Double-edged sword.

You can argue that forced upgrades put people in the left seat who don't want to do it and maybe aren't up to it.

But you can also argue that forced upgrades put the most experienced pilots (on average) in the left seat, rather than letting them bypass and pushing upgrade further down the list to less experienced (on average) pilots. AA mainline had a mandatory upgrade policy for a long time... you upgraded when a few people junior to you took it.

And fundamentally, airlines hire people to be CA's... they shouldn't be hiring anyone knowing he/she is a career FO. And you shouldn't take the job expecting to be a career FO either... odds are good you can do that if you want but junior-manning happens sometimes.

If you wanted to mostly ignore seniority, you could come up with an arbitrary junior-manning scheme which prioritized pilots based on their experience... TT, 121, turbojet, etc. So instead of upgrading a CFI at legal mins because his number came up, you could instead upgrade the guy with 10K and previous 121 TPIC, etc. But again, seniority.