I didn't say TM procs RS. I said it procs unload and unload has a 75% chance for a free RS. And by free unload I had meant the cooldown, and not heat. That was my fault.
Essentially, you're trading a rail shot every 6 (75% of the time) seconds or every 12 (25% of the time) seconds (averaged out at every 7.5 seconds) for the 6% damage from arsenal. And since arsenal outdoes pyro for pve dps anyways, it's just in comparison to that.
So the differences would be: No heatseeker, no 6% damage boost, rail shot to be used on average every 7.5 seconds (half the cooldown). 6% crit chance, dot from combustible, lose out on 30% armor ignore from hv, but gain 30 for unload and 100 for rail shot (main two moves anyways). Heat could be more difficult to maintain, but with the changes to alacrity it'd probably be fine.
Short version:
Gains: 6% crit - RS CD halved - Incendiary for some movement - Combustible DoT - Decent Armor ignorance
Loses: Heatseeker - 6% dmg - Decent armor ignorance - Heat management
Edit: I forgot about the gcd imposed by rail shot for some reason. RS CD would be cut by 40% on average and not 50%. Still significant.
