1. I agree that TP being a No. 1 option on a championship team is still a big question mark. He's playing damn well but I don't know if he's physically capable of reaching the LeBron, Prime Duncan, Prime Shaq level.
2. The OP was talking about who is the best PG. What contender has CP3 defeated in the playoffs?
3. Parker was the best player on the Spurs in 2007 vs. the Suns. His Game 1 performance probably was the most important performance of the entire playoffs that year for the Spurs in retrospect. The Suns were probably the 2nd best team in the NBA, so it sounds to me like that fits your criteria.
4. This is the first time I've ever though TP is the best PG in the league. Right now, it's not really debatable.
5. Being the best PG in the league in February doesn't mean anything so, yeah, still a long ways to go.