I agree with OP. In Halo 3 If you got into a BR fight with anyone and you missed or you notice they are playing well as a team and leapfrog, you should be dead because they premeditated their attack. Since there were no AA's you were FORCED to stay in and fight it out because you know you can't get out fast enough. Let's be honest, this scenario has allowed for some AMAZING clutch plays if you were good enough, only because you knew you had to TRY.
With AA's such as sprint: you get into a DMR fight and you simply weren't feeling it and miss or they leap frog, you should be dead, but oh wait, let me just sprint away and completely nullify the good setup and positioning the other team had. IT IS SUCH A CHEAP MECHANIC!! Cheap. You don't attempt to try to do anything clutch because you can easily gtfo. In terms of fun, I believe pulling off a clutch play is FAR more rewarding then saying "ooh I have sprint let me run away." However, these kids seem to just want games to be dumbed wayyyy down,simplistic,easy, and casual.
In my opinion, Halo 3 seemed to have a MUCH larger community than Reach. Everyone I knew played Halo 3. When Reach came out, Halo slowly dwindled down in popularity. So, basically I just wanted to emphasize on what the OP was talking about.