Sooner or later, the computer will figure out that all its accomplishing by sending more terminators is that John Connor soaks up more XP. Skynet must do what computers always do to keep humans humble – cheat. What they should do is send a borg back that can set up skynet way back in the past before John Connor is born. Also, if it can, it should corrupt John Connor’s saved games.
Actually, that’s a really interesting point. It could be argued that the only reason John Connor is the savior of mankind is because he fought off a million terminators growing up. IOW, Skynet created and trained its own nemesis.
Per the first and third movies, that’s definitely the case. Sarah raised and trained John to be the resistance leader (and in fact he was only born in the first place) because of her experience with Reese and the first Terminator. It’s only T2 and Chronicles that imply that the causal loop can be broken and John doesn’t have to have that future.