I get what you're saying and you're 100% right. As for the reasoning behind why I made the choices:
SFX I ran out of time to implement properly, so I discarded most of it. The issue is that most turrets shoot at a rate of 2/sec, and you can have up to 50 turrets, which would make it just a constant "bleep". As for visually, at first, I had flying bullets, but it was programmatically much easier/faster to add effects to an instant hit, and I had less overhead on calculating bullet pathing (Again, same problem -> instant hits = easier), and it took little to no time to setup without bugs (compared to bullets with special effects).
Now if I let the bullets just fly without pathing, then you start missing shots, which felt like a punishment and wasn't fun. If I speed up the bullets so that they don't miss, they fly so fast that you won't even see them, which would make them equivalent to instant hits.
The cleanest way to convey the info would then be like you mention a particle effect for an on hit, and prototype a bullet with tracking.
For debugging I added logs of the damage done per turret, perhaps I should make it accessible in the ui in some form that it's clear what's doing the most dps.