Sagittarius like you noticed is very inaccurate so it misses often on sustained pd duty and hits armor a lot on hull busting duty. It also costs more op than the thumper, less efficient, less accurate, has lower hit strength, less burst dps, and, if you smod expanded mags, less sustained dps. Honestly, it could use a buff I think.
ER particle guns have a pretty high refire delay compared to other PD options which means they can be saturated quite easily. It's not really meant for pd anyway and more for hull busting. Also 8 freaking OP. But for high tech who lack good long range small energies, it's a nice option to have. Compare to the tactical laser, you are paying 4 more OP (and some flux efficiency) for hard flux damage and superior hull damage.
This theme holds true for many of the imperial weapons, pay more OP and get some benefits with some drawbacks. Telum autocannon: More hit strength and slightly more dps than heavy autocannon but worse efficiency. Solis cannon: More dps and hit strength than mauler but worse efficiency and range. And so on. If you can afford to mount them, they are good. But if you can't, vanilla options are better.
