Sci-Fi settings where people have shields (like Halo which did and Mass Effect which didn't) are good for dealing with the headshot power vs. realism conumdrum. Massive Dmaage/instakill while shields are down, regular damage or only very slightly more while they're up.
Mass Effect totally has shields.
On-topic: I picked a fight with the Ancient Guardians. I had the single mightiest non-Guardian military in the galaxy, I had dozens of experienced troop units, I had defense batteries orbiting my worlds, and more importantly the game would be ending in a year and I was comfortably in the lead. So I decided "what the heck, it's only one system, I'll rush them down, bombard Utopia for a while, then invade".
Immediately after the DoW, I get multiple reports of Guardian fleets attacking my systems. I was getting hit by such huge fleets, each spewing hundreds of projectiles and launching dozens of fighters, that my none-too-shabby desktop was stuttering. Defense batteries and mining stations were either obliterated with ease or captured. I snuck a few invasion fleets into the Guardian's system, hoping to capture Utopia or at least distract the rampaging fleets, but they had at least two dozen ships in reserve. Not a single troop managed to land.
All I could do was watch in horrified fascination as my mighty military was driven back, most ships dying quickly while a few survivors limped back to systems still under my control. That's when I noticed that Guardian ships can actually catch up to my ships in hyperspace...and even shoot at my ships. While passing. In hyperspace.
All in all, I think I maybe destroyed half a dozen Guardian ships. Mostly badly-outnumbered escorts. I lost more than a dozen fleets.
Distant Worlds: Universe.