As a fan without any finance or contract experience I have to say the deal doesn't look all that great to me and I doubt an agent would of let him sign such a deal. With the leverage he had he needed to sign a 6 or 7 year deal that had more than 2x up front and guaranteed money to protect himself from injury. I haven't seen the deal but on the surface it looks like he screwed himself and possibly cost himself 10's of million of dollars, big mistake not to have an agent negotiate on his behalf.
Again as a fan I see Tunsil the player having all the tools in the world, far better than what we have seen come out in 2020 except possibly Wills, that said Tunsil has not excelled into the best offensive tackle in the league as one would expect. As a novice scout I would put Tunsil's value at 16-17 mil a yr and as a GM I would of liked to have signed him to a performance based contract to motivate him, although with FA your forced to over pay players like Tunsil.