Some numbers for context:
Heavy gun rebuild with spanner: ~ 10s
Light gun " " : ~ 7s
Time for heavy gun to burn out: ~35s (20 stacks, goes up to 40s if you reduce it to 17 stacks)
Time for light gun to burn out: ~17s
Time to chem guns from 20 stacks to < 8: 25s
Using pre set heat sink saves 5 seconds of your engineers time and more if it stops the full 20 stacks from being added, buffing it to -4+ stacks per reload would improve that to 10s (because rounding)
Fire stacks are apparently better at gun disable than just breaking it. Imo they should be (if not as much as they are) because you cant stop artemis etc with chem. It wouldn't take much to make burning out and rebuilding better than chemming down in most cases although im hesitant to agree with any buff to fire damage