deetrArxI played TFC for 8 years. I didn't like the idea of TF2. I saw a load of videos and hated that they took all the speed out of the game. Sadly I had to move to TF2 as TFC was dying and I still wanted to play a game that had some of the TFC characteristics. I feel like Overwatch is pretty much the same thing happening again. Imagine going from this to TF2: https://www.youtube.com/watch?v=hOyGGs9s2jA
I disagree with this because of exactly what you said in the rest of your post. Overwatch is more moba-like than FPS-like and I don't think that there will be enough in common for the TF2 community to migrate many players completely.
This game is extremely similar to tf2, I really don't understand why so many people think this game is going to be LoL: The FPS. The big similarities between overwatch and moba games are the ultimate abilities (which aren't purely based on cooldowns) and the active abilities (like shields, damage buffs, etc.). Infact, the ultimates in overwatch are very similar to things like an ubercharge or a buff banner. The rest of the game is pure DM and usage of mobility options.
It's already announced that the game will be played 6v6, with control point/payload maps, with no class limits (atleast in the beginning). And the fact that there will be a mixture of hitscan and projectile weapons, the players who will be best suited to adapt to this game will definitely be TF2 players. We're already used to playing around ubercharge timings, offclassing, and the pace of CP/Payload maps. The way I see it, this game is basically TF2, except it has a lot more classes and each one of those classes has a game changing ability like an ubercharge.