Fair. But they're still paying a cost for something that doesn't really gain them much. They'd win the Constructors with just Lewis running at this point.
Suppose you could argue the earlier experience is huge for Russell but how much is that actually worth?
There is a case to be made for sponsorship reasons. This season I think Mercedes has got their fair share of TV time, but in past years (same can be said for Red Bull during Vettel's dominance, and Schumacher in the early 2000s) the race starts and then you don't really see them until the pitstops. Someone did a breakdown of this years ago, I think it was Japan 2015 or 2016, and Mercedes was on the broadcast for like less than 10% of the race. IIRC Mercedes complained about it after the race and the next race they had more TV time. Sponsors pay big money to get their name seen and the bigger the team, the more money it costs. Where I'm going with this is, that ever since Rosberg left after 2016, Hamilton vs. Vettel was an okay storyline for a while and then Hamilton beating Schumacher's records, but Bottas is one of the worst drivers on the grid when it comes to creating PR hype for the team. Basically he's too much of a nice guy to do anything that goes against the team, and even if he manages to screw up, he's the first guy to raise his hand and apologize. Russell looks to be more ambitious and doesn't hide it, also somewhat arrogant in a good way. Idk if Mercedes would still let them (Hamilton & Russell) race, but I feel Russell would be more inclined to ignore team orders and do what's best for him. I mean, we've seen Bottas for 4 seasons now and every time it looks like he's getting closer, Hamilton finds another level and pull away even more.
I actually talked about Russell to Mercedes for 2021 with my dad before the weekend, and the only currently available path that I came up with was:
Russell to Mercedes
Perez to Williams (there was rumours about it months ago, and Williams would probably prefer the extra money Perez could bring)
Bottas to Red Bull (veteran number 2 with top team experience to replace Albon, and RB can easily cut ties with him after one season if it doesn't work out)
I don't see Perez to RB because I think he'd want more than one year and considering how unreliable RB's second driver has been, would they give anyone more than one year?