I don't think things would have changed that drastically. The ps3 may have sold more, but not nearly as much as you say.
If the ps3 was really that much less powerful than the 360 it would also have a huge effect of 3rd party developers as well. Maybe some developers would have just stayed just with 360 because they knew the ps3 couldn't handle X game. Or like you mentioned, some 3rd party games like gta4 would have sold better on ps3. Maybe developers like Quantic Dream would have made Heavy Rain exclusive to the 360 instead 0_o
If MS was in 3rd place they would have definitely been more aggressive on pricing and exclusives.







