Peguy is a better option in the middle than Cahill, if you're looking to hold the ball or connect passes. He's just not as good in the air, where Cahill is like an extra center back when defending set pieces.
Akpan might have made RSL think twice about giving us room on the flanks, since they were quite comfortable keeping BWP away from anything in the air. Hell, could have thrown in Miazga and played five at the back or bumped Sekagya into midfield to let Cahill play up top.
There are always options. Petke seems frozen when the result is close. He knows what to do if we're winning easily, and he knows how to throw everything at the game if we're losing. But seems to me he gets stuck when games are tight.
Bottom line seems to be he just doesn't trust most of the guys he has on the bench. What's odd is how zero-sum he is: guys are either starters or they're nothing. Very little in between.