For sure Hamilton is quicker but as Mr Jack also mentioned - If Hamilton wasn't there Mercedes would still be winning.
Actually, I realise I got my sums wrong. I accounted for Bottas getting extra points, but not Max. Remove Hamilton, and you have 4 wins and two 2nds for Max vs. 3 wins and three 2nds for Bottas. With Albon being so potato, Mercedes might be ahead if their second driver was closer to Bottas's skill.
I'm pretty sure you could put any of the F1 drivers in the Merc and they would be winning too. My point is you have to question Mercedes spending $50m(?) per year for Hamilton when they would win with drivers on a much lower salary.
I'm pretty sure you couldn't. It depends on where you rate Bottas, but I think he's in the better half of drivers on the grid. Not as good as Ricciardo, for example, but better than the likes of KMag, Grosjean, Pérez or (at this stage in his career) Raikkonen. Bottas is behind Max on points, so I think you'd need one of the better drivers to be ahead of Red Bull. Last year, Mercedes were stronger I think (although they had more competition since Ferrari still had their good engines), and pretty much any of the better drivers could have got there. But look at '17 and '18. I'm pretty sure that almost any other driver would have lost to the Ferraris those years. Bottas was 3rd in '17 well behind and an embarrassing 5th in 2018.
Mercedes don't know what kind of season it's going to be before it begins when they're choosing drivers. Maybe it's a season like 2019 where they're towering over the opposition, or maybe it's a season like 2018 where Hamilton makes the difference between 5th and 1st. They're paying for the best driver in order to make sure that they can win regardless of what kind of season it is.
Another thing to consider is the brand value of a driver like Lewis. He brings a lot of sponsor interest, and marketability to the team. That's important to any team but especially to one like Mercedes that is partially a marketing exercise for their more important road car division.