That's all well and good until you remember that Stones is incapable of staying fit and is therefore useless to keep as third choice.I’d actually keep Stones as 3rd choice CB if we sign Koulibaly.
Stones partnered with Laporte or Koulibaly is a good player.
Stones partnered with Otamendi or Garcia is an accident waiting to happen.
Ideally both he and Nico would leave but I don't think that's realistic, so if one has to stay I'd prefer it to be the one who's pretty much always available for selection, since that's the entire point of being a backup. Stones has only 1 year left on his deal and I can't see an argument for giving him an extension. He's at a good age to sell and is homegrown; sell him to Everton or Arsenal and take what we can get for him. Nico's deal also expires in 2022 but he's old and has wage demands that most clubs will struggle to meet, meaning he'll probably fail to find a club like he did last summer even if we do try to sell him.
Also at least when Otamendi fucks up it's kind of funny because he's just so ridiculous. When Stones makes a misake it's just sad because you're reminded of how mentally fragile he is lol.