It's not pointless. The Compact Thrower is a stunner to the regular Proton Pack's entangler, something you could use alongside the regular Pack to knock the wind out of a ghost if it's proving difficult to wrangle into a Trap.
On top of that, it can either give a Ghostbuster a greater degree of flexibility, to mitigate the amount of damage that could be caused to an area (especially if it's a very expensive location like a museum full of priceless artwork, or a store full of delicate crystal).
In the end, we have to remember that the device was likely still in the prototype stage, and it didn't have a fair chance to make its mark as Garraka was able to freeze the proton streams. Against any other ghost, it probably would've shon.
