Heupel may or may not need to go. I wouldn't know, but I do think he ought to have ultimatums with teeth. I hate it for the younger coaches that are not making "never work again" money, but they know what they are getting into, and they are chasing a dream. They accepted the risks - I feel for the families. The higher paid coaches are big boys making big, BIG boy money. Put up or pack out.
What you are hearing/sensing/seeing, is a fanbase that sees a head coach out of his depth in one or more areas. That is a huge red flag.
With the resources at his disposal-
Heupel either:
1) Can't see the problems that have been present for at least two seasons, or
2) Doesn't know how to correct the problems, or
3) Doesn't care to correct the problems, or
4) Won't do what it takes to correct the problems
... or a combination of the above. The problems on Defense, defensive player recruiting, offensive scheming, Strength and Conditioning, and the most basic of all... tackling... are real. They have not been addressed. Many of those deficiencies have very little relation to the complications of NIL or the transfer portal. They are internal organizational failures.
The problems are not top secret. They are not difficult to point out. None (very few?) of us coach college ball for a living, and certainly none of us coach D1 ball for a living at that level, and yet the same deficiencies have played out each game - with different student athletes - over the last two seasons. (at least).