Why couldn't Philip beat the hell of the Infected?

[Thaliur]

And the Tuurngait are not even human, so it might not be possible to judge them based on looks.

Yeah they are!

I guess "They were" would be better. They have been extensively altered by the Tuurngait virus, and about as human as a common borg drone, at most.
I'm not totally certain about it, but I think there were some notes saying that the infected people became immensely stronger and more resistent to anything than they were before they turned into Tuurngait.