See, what you're suggesting here is called "telegraphing a suicidal strategy" and by burst you basically mean "an all-in attack as soon as pantheon is level 2" -- while pantheon+ranged carry can pull off such a strategy vs soraka fairly well, if they **** up and die, that's it, they lose the lane and the game is almost guanrateed a loss, or at least, a huge uphill battle. This is why farming is preferred, because then the game won't swing so widely so rapidly and players will have a better chance at winning.

Any smart Soraka player will tell her ad carry to hang back against such a lane and coordinate with their jungler to cripple the lane. Pantheon likely won't be able to start with many wards, if any at all, and if he gets harassed even a little, he can't really commit to a kill! He has to go back and heal if he wants to do that. Your strategy is risky and not an actual counter to soraka, of which there really is none. W's armor component alone, on someone like Graves or Vayne, is more than enough for the ad carry to kill someone before they die (and thus win in the end) against the kill lane's AD carry or their "support".