If you're working against the clock in any fashion, or facing overwhelming odds in your dogfight the loki isn't worth that much more.
The 'excess' manuverability it holds is, excess, you can get an eri to turn about as fast as most people can turn a loki if you fly it properly, and the eri has about 10x the firepower, comparing the two isn't a great idea because they're there for different reasons.
If this were an RPG and you could taunt and keep agro of all the enemy fighters the loki would be lovely, cuz then you could let everyone else blow up what's shooting at you, but with only 4 banks (primary) and a small secondary bank you lose a huge, huge amount of firepower, and you will quickly see your squad vanish into small explosions in the night sky if you aren't helping (well, on well balanced missions).
The loki DOES make a decent interceptor, but it's really not space superiority, it doesn't have the 'oomph' to make the difference.
Wheny ou consider what you can load an eri out with compared to a loki for a little loss in unneeded defences against most ships/scenarios you'll want the eri.
The loki would beat the eri 1on1 though - assuming equal and respectable skill levels on behalf of both pilots.
Well, assuming the eri doesn't blow the loki up in one pass.
I would be trying for that if BD were coming at me in a Loki -.-