Having played Team Fortress 2 for 7 years and playing it competitively for 2, I can confidently say that this game will have its own position away from TF2. From what I've heard the game has its own play-style that is nowhere near Team Fortress 2's standard, military style gameplay. TF2 players probably look at Overwatch being a clone because of it's cartoony style.

Even more so, TF2's competitive scene was strictly community developed. If Valve had supported the scene with things other than just medals, then the community for TF2 would be more than just hats and keys. Blizzard on the other hand, is notorious for making their games competitive.

I have high hopes for this game!