Serving could be key especially for an attacking player. You wonder if Fed would have continued to stay at the top of the game with these super-fit grinders if he couldn't serve his way to cheap points.
Raonic has enough ground game and talent to win return games. I like Kei but not sure if he can win cheap points on serve and also he can be erratic sometimes still. I hope they both get to the top though.
True, Milos's serve is a huge weapon, but especially on the current slow surfaces that can only take him so far. Kei has much more to his game imo: he's an exceptional returner, moves great and is a far more solid and creative shotmaker than Milos, not to mention he does quite well at the net too. As you saw in this final, as soon as a rally started it was all Kei. If he's already this good without getting any free points on serve, just imagine how good he will be when he beefs up his serve a bit, which is certainly achievable.
I do agree that it'd be nice to see both rise to the top 10 and then even higher though. Milos's brand of big serving tennis with aggressive groundstrokes belongs at the top too, but I do believe Kei is a far more complete talent with a higher ceiling.