re: Interior defense looks scary bad....gaping holes to run through.

An offense / defense scrimmage favors the offense by a lot.
In anormal game, an offense might never sub: same 5 OL, v minimal WR changing and ocasional RB swapping. They can survive more.
For a defense to function, you need a lot of bodies. There is a frequent DL rotation 2 sometimes 3 deep. Also, LBs and DBs are running all over the place and may need breathers. In a second half once those DL rotation players are 3rd stringers and they’re not in fall time shape, the RBs and OL will feast.
We saw the DL do v well in the beginning of the game