QB pay sucks right now, but the one good thing in this situation is that it basically escalates based on timing more so than actual play. So even if he's MVP in 2025, he's probably getting about the same deal anyway (and if he stinks or just average, you say goodbye). Jackson is the 8th highest paid QB, Mahomes is 12th and Allen is 14th; as designed, it's not based on merit.
So, if there's still some question, I think the best move would be to franchise tag him and if he proves to be an elite QB, then do the deal the following year in 2026. Based on the past trends, it will be about 5M per year more than it would have been in 2025, I can live with that as it will still basically be market rate and you'd have that extra year of evaluation to see if he's legit or a fluke.
After all, if they turned the keys to McCarthy, he'd already be looking at a new deal in 2027 anyway.