Which number specifically?
If his cap his is 23m that is about 8.6% of this year's 198m cap.
Pace actually carried a 7m average cap hit per year on the deal for him as well which would be identical to Bakhtiari's 8.6% and he was the 3rd highest paid LT that year. Don't get me wrong, it is a lot of money, but it is about as expected for a player who is arguably one of the best at his position and at that specific position.
As far as QBs go, I'm looking at averages because bonus structures are complicated year to year with their cap hit. Watson, Mahomes, Wilson, Roethlisberger, Goff, Rodgers, Cousins, Wentz, Prescott, and Ryan all carry an average over 30m. Tannehill is just under at 29.5m
If the cap goes down you will see deals get pro-rated with it. If they don't do that half the league is likely over a decreased cap number already before we even hit FA. Over the cap is projecting a 176m cap (where that number comes from I do not know) and that puts the Rams for example 23m over and even worse the Saints at 98m over (how they will fix that I have no clue).