His Oregon salary isn't 5.5 million. It's an average of 4.55 million under the new contract. At its peak, if he hits the incentives, he gets the option of an extra year on his contract that is worth 5 million (which in S Fl is equivalent to paying him about $4.4 million due to no state income tax). The bonus option year is typically going to be the highest salary, otherwise it makes no sense to include it.
If you mean Miami is going to have to pay him at least 5.5 m, it's possible. But consider what would have happened if Blake James master plan had worked out like he hoped and Diaz had been successful. Diaz is supposedly making around 3.5 million right now. If hypothetically he had won the ACC coastal this year, I think we all know he would have received a contract extension that would have bumped his salary up to probably around 4.5 million if not more through 2026 or 2027. So there would really only be a 1 million salary difference between the two coaches.