Because now YJIT is deprecated and at some point in a year or two I will have to have my team go through and switch everything from YJIT to ZJIT. So it's creating random tech debt busywork that will suck up dev resources that could better be used building features.

In isolation, having to switch from YJIT to ZJIT isn't that bad, but this same type of churn happens across so much of the frameworks and technologies that my company uses that in aggregate it becomes quite an annoyance.

YJIT is not deprecated. That word has a specific meaning in Ruby. You can continue to use YJIT.

With any luck, this performance in the next year or two will be enough to make it a happy change. "Damn, free money" etc

Most JIT compiled languages have multiple implications, each pushing each other forward.