Main reasons why the sniper Domi has slowly fallen out of being a highly suggested pick include:
Requires a MJD to even be functional, thus not usable by anyone under alpha clone status.
Ditto for the fact they cannot use sentry drones. Which is compounded by the long range sentries being low DPS.
Requires significant trade-offs to fit because to get your damage relevant you must shield tank it.
Spending three times as much gets you a rattlesnake that does twice the damage and actually has a solid tank.
The Gila is something of a overpowered as hell ship for PvE doing 700+ DPS from a cruiser sized platform and can work near the edges of what your sniper Domi would get effective sentry damage from. When a cruiser can do more DPS, get through missions faster, travel between sites much faster…
Basically its mostly a case of keeping things stupid simple like a basic cruise missile raven that can be slapped together for ~180-190m or going for it and getting a rattle or nightmare for significant high range damage. The other side of the spectrum is really more interested in machariels for that mission blitz speed.