I know everyones situation is different. For mine, Frontier just lost their competitive advantage to United Mileage plus. I am summit and Premier Exec. I fly quite a bit to PHX. If I receive 2,408 miles on United Round trip (with 100% bonus being premier exec) it takes roughly 11 trips to amount 26,488 miles (one free ticket). If I fly frontier to PHX I receive 1768 miles (50% bonus being summit). I takes roughly 12 round trips to have 21216 miles (one free ticket). I'll call that a wash, but for me Frontier's change puts them in the same as every one else's bucket.
I will still fly them but not as much. I will fly enough to get AScent this year while still maintaining Premier Exec. Next year I may have to put all my eggs in one basket and go for 1 K. Not sure.