Microsoft doesnt have very much to counter. Their wallet does most of the work for them rather than their internal abilities, which means Sony should be wary but not extremely concerned.
If Sony makes games Microsoft cannot answer to like Uncharted, MS will keep making acts of desperation to prove Sony right.
Its not about being behind Sony, its also about naturally not being able to follow them despite what they already have right now. Wait until Sony unloads their internal games at MS. They wont be able to follow. Sony is going to prove them to be more creatively handicapped than they've already shown with Tomb Raider's temporary exclusivity. ;)
Sony should not forget about Halo, but rather focus on what matters until their answer for Halo comes. During the PS3 era once Sony bashed MS with exclusve after exclusive not one FPS hit the mark but all the other genres did fairly to very very well. This speaks volumes. They need to stick to what works until they get to the level they demand for shooters.
Maybe Sony needs to be like MS and scount an outside companies Shooter then buy the company.