I fully understand your point. I think we had lesser flaming here in the boards with all the MP modes in a separate patch after the release like in HL2. SP is/was what make the money for GR and GRAW, modding keep the game alive.
For the game modes I like to play with mates against AI. Why? It's because not trouble with cheating, AI use some known tactics, real people tend to do things in games they never do in RL. Like suicide attacks, intentional TK's ...
Ok, in a trained squad against another trained it makes sense, but I'm playing for fun and try to relax I'm not playing professional.