It's one of those things where you can't even say one has something over the other. I'll link their wiki stats here:
Lets start with the physical damage:
Frag shot: 147(0.4power)
Both hit in 120 around the target. I have tested this. Both can crit. Blatant advantage to shattershot. Not even close.
Attack speed: Shattershot comes out about 0.67 seconds, fragmentation shot at 1.2, nearly twice as slow. Projectile speed difference seems negligible. The arc of shattershot does seem slightly useful in situations that you are firing uphill. For physical DPS, renegade shortbow is at least 2 to 3 times better, just considering these factors. But pistol is a condition weapon you say! (So is shortbow hahaha). Let's move on then...
Frag shot: 5 secs of bleeding only on the primary target. (Pre-release data showed this once was AEO bleed. Removed for full game.)
Shattershot: 3 secs of bleeding in the full AOE.
Everyone knows they would rather trade 2 secs of the bleed for AEO cleave potential. Especially with how much faster it comes out. Granted! You can boost pistol condi durations by 50%. Arguably worthwhile, but any engineer player knows they are not stopping to auto here. It's for blowtorch and then time to swap kits.
Both have the same range. They are clearly very similar skills in theme, but it's just obvious how Renegade btfo's pistol engi when you look at traits.
This might seem like a pointless discussion, but to me it's an outright ripoff that an elite spec basically comes out with an entirely better version of a skill. Forgetting about old skills is how we got here. Renegade as a whole feels like a much better version of the entire firearms trait line! A 33% crit boost from not dodging, entirely outdoing the 25% you can get from firearms, very easy might generation from any critical hits, plenty of bleeding bonuses, and even lets the autoattack pierce. Automatic fury generation regardless of range. Let's just say it: power creep. If you like pistol engi but want more oomph, pay up.
Ever notice how skill 4 on both weapon sets burns? 5 is a CC? 3 multi hits? See where I'm going?
As the final nail in the coffin, renegade can summon mortar fire from better engineers from the mists. Bruh. And turrets are still useless despite being the LAST actual machine that engineers can really even put out in the field - 1000 hp function gyro does not count. It's not funny anymore. Core engineer/scrapper is begging for that kind of quality of life and synergy. It's pleading for skills that define its class and give it that unique edge. As it stands, engineer is better called a weaponsmith or chrono lite. It builds no fortifications, no useful machines, it's all wells, prime light beams, and flamethrowers. I am not excited to play this game with my main being a confused damp forgotten noodle.
Society either needs a turret rework or to free bobby schmurda and I wonder which comes first?