So, the first question is
How do you define "winning" in a MMO?
Personally, I define it as completing top tier progression and excelling at ranked or rated PVP. Anything below that is filler content. Now, I love filler content. But when I find a datacron I don't think to myself. "Yeah! I just won at swtor!"
What items would have to be in the swtor item shop for you to consider the game P2W?
Current tier PvP and PvE sets. Anything below current (right now campaign and war hero would be current) isn't competitive gear and thus isn't winning.
What items do you not consider P2W?
Anything that isn't useful at end game. Exp pots, BOA leveling gear like from WoW, cosmetics like color crystals or moddable sets. I would go so far as to say a level 50 "starter set" (Ilv126) that breaks after 30 days. I've seen these in vindictus a lot. It works pretty well.