I used Melanie's Olympic Timer as the basis for my code and she included some of the things that you have advised against such as adding the SetTimer subroutine call in the Starttimer routine and INTCON.7=1.

i should address some of these issues when using on interrupt


subroutine call in isr
pbp code is not re-entrant if the isr is called while the foreground task is running the same routine the result will be unpredictable
subroutines in an isr are bad practice mostly

INTCON.7=1
pbp on interrupt is not a real interrupt , the int flag is simply checked on completion of every command with flow diverted if flag set
if you actually enable interrupts where does the int vector point ? not good not needed