Bottas is far too good of a second driver, for far too cheap, to drop from Mercedes. Should Ocon get a seat? Absolutely. Should he replace Bottas? Not a chance. Bottas is still second in the championship right now. Why would you drop that from your lineup?
I wrestled with this one, I still think Bottas has a chance to keep the seat but there is a few things I see that lead me to my thought.
1. Bottas finished 5th last year with what I think (and probably Mercedes as well) is a far superior car to the rest of the field, he 30 in a week and Merc needs to see if the can find Hamilton's heir, and it is not Bottas.
2. Sure he is second in the standings, but Max should pass him with Vettel and maybe even LeClerc with a chance if he continues with poor performances. He really needs solid runs in the next 3 - 4 races to get a contract, even then next point.
3. Ocon is a lot younger (yeah I don't know if he is the next #1 Merc driver, but as said they have put a lot into him, better to try now than wait until Hamilton retires to find out)
4. Wolff seems to be holding back on saying much about Bottas future and has even said he wants Bottas to have a "soft landing" if he is let go.
5. Bottas himself has been talking to other teams.
I agree with your points, but Merc doesn't need a cheap second driver, they need someone who can win a championship once Hamilton is gone. There is a possibility they could go after Max, but they would not leave it up to chance IMO.
Get Ocon in the car, and see what he can do.
Regardless Bottas only gets another year if he does stay. Just keeping the seat warm.