If you think the 5-12 was just because if injury, then just taking Carr off the roster does not mean you are tanking. Frankly, if the roster really is around a .500 roster, and I think it is, we probably have just as good of a shot of making the playoff with Rattler or a young vet like Jones or Field, as we do with Carr. So I don't understand why you seem to think cutting or trading Carr would be trying to tank. It may end up in a losing season if guys can't stay healthy, but that's going to happen regardless of if Carr is the QB or not. And, as I have said before, Loomis has for the last few years spent very little on free agents outside of Carr. Whatever the final number goal is, it's clear that Loomis wants to get the cap better under control so he isn't likely to spend big this year anyway. And, as you suggest, the cap is really for signing your own good players that you drafted so, why would it matter if we don't have cap space to sign free agents this year?
The advantage of parting with Carr now is that you start the search for your franchise QB in year one for Moore and you create more cap space to sign the few good young players we have to extensions next year, while also having a bit of money to bring in some mid-priced guys to help build the roster the way Moore wants it. We can't do any of that this year without kicking the can on Carr's contract and/or other contracts and for the last few years Loomis has been unwilling to do that more than is necessary to get cap compliant. Gone for now are the days of creating as much cap space as possible by kicking the can. And, I expect they won't be back until we find a franchise QB.
We might as well start that process of finding a franchise QB in year one for the new HC. To do otherwise would not be fair to him because coaches succeed or get fired on their ability to find their QB. No point in not letting Moore get that process started this year rather than in year 2 when he would be another year closer to being fired because he hasn't found his QB.