I disagree, at least until someone proves to me otherwise. If you feel "bad" after diving with air I think you're doing something wrong. I "think" you can change your approach to diving and feel much better.
I would rather dive more conservatively, go into deco, and ascend much slower than just arbitrarily throwing nitrox at the issue of feeling "tired". When someone tells me they always feel tired after dives my 1st go to is how do you ascend in the last 20', how hydrated are you, etc? Not.. "oh hey you should dive nitrox, you'll feel much better". While it might work I don't think it's the correct approach.
Hence the discussion.. maybe I'm wrong.
This is basically how my conversation went on Sat. I said something along the lines of you can get the same results changing your approach to diving vs just throwing a bandaid on it and diving nitrox. I asked him what type of gf's did his buddy dive, how fast does he come up, etc.