The top driver field seems to be saturated, and while Bottas is good, he doesn't seem to belong in the top bracket.

There are 4 big teams, 1 of them isn't very big at the moment, next year they might return to some glory. So at most, next year there'll be 8 top seats, logically those 8 seats should have the 8 best drivers on the grid, so which are the 8 best drivers? In no particular order, I think the list goes something like this:

Hamilton, Rosberg, Alonso, Vettel, Ricciardo, Verstappen, Vandoorne, ???.

There is an empty seat. I guess my point is that it's debatable whether Raikkonen belongs in the top 8 anymore. In any case, while he's not as good as he once was, he seems to have improved his form, and that might be the key to say whether Raikkonen deserves a top seat or not. In any cases the list of drivers I think could be fighting for that seat is: Perez, Magnussen, Bottas, Raikkonen, Wehrlein, Ocon, Kvyat (pre 2016 anyway), Sainz. Of these drivers, It's hard to pick which one is the best and there's even newer drivers coming into f1, Stroll for example.

I guess if Bottas did get that 8th seat it wouldn't be a bad decision. There's no obvious talent right now that deserves it, at least not yet, but unless he proved otherwise against his top teammate, I don't think he'd stay in a top seat for very long.

If Button stayed, then I would definitely say no. He wouldn't deserve having a top seat over any of those 8, but Button leaving left the top 8 drivers with a vacant spot. Perhaps Raikkonen still deserves that spot, he definitely seems to have cleared his patchy years of 2014 and 2015 somewhat. In any case, I have no confidence in Bottas to say that he deserves a top seat. But it wouldn't be a terrible decision. If Ferrari want a replacement and want a good number 2 driver that scores consistent points and isn't challenging Vettel, then I'd say he's probably a very good choice.