Should Rattler be our starter in 2025?

Yep. Not even close.

It's not a Superbowl roster. If we were truly ready to compete, yeah of course you go with Carr.

But we're not remotely close to competing. So, you take your medicine on Carr's contract, and you trot Rattler out next year. Either one of two things will happen:

He'll have developed nicely and plays well, putting us in a nice spot to build around a good QB on a rookie contract. Or, he didn't develop nicely, and we're bad; positioning us for a top pick and we can stack assets until we do find our QB in either 2026 or 2027.
There are definitely two different trains of though on this and no real middle ground. I am with the train you just described above and the other train wants to win as many games per year as possible, even if that means only 5 wins are possible again.