That's definitely the case IMHO also. There's a huge difference between guitar tones in a mix and out of a mix. I find that the more your ears get used to tweaking outside a mix you tend to go darker and darker. I like brighter guitars in a mix. Also the "juicy mids" seems to be my signature thing or at least that's what people say when talking about my IR's.Glad you are hip to the SM57. It is a classic for a reason. It is easily my favorite mic. I will usually blend in a second to add some depth/flavor but if I only get one? No contest.
I find a strong majority of the IRs in the stock set too dark, FWIW. I out this down to personal pref though, no right or wrong.
SM57 is the majority of your tone. Other mics are IMO blend mics but sure I make them sound as good as possible on their own as well.