Honestly? I really can't see how anyone could go for that option. But thanks for at least answering the question.
I'll try and expand on my answer.
Firstly, I can't deny that Sane, Kante and Gundogan would have been good signings, or will be for their new clubs. But then again they might completely flop, we just don't know.
Sane in particular we don't know how well he will do. We signed the top wing talent going last year in Memphis and that hasn't worked out so far. I think he's far more of a punt than Mkhi.
My biggest problem with your argument is that you're forgetting we still have a a lot of players who would need to be moved on to accommodate these signings. We still have Herrera, Schneiderlin, Carrick, Fellaini, Schweini (

), Mata, Lingard, Young, you could even count Januzaj and Perriera in that list.
Some of these players just don't want to leave (or there might not be any takers so we're stuck with them for now), and while the players you mention would be upgrades, especially as most of those I mentioned could be considered 'squad' players, it would mean a fair old overhaul. I would rather they were slowly phased out of the club and replaced over the course of the next few seasons.
It may turn out that your argument is completely correct, but for now I'm sticking with option A as the best path for the team.