I think you're all missing why he wants Mount. Carl Anka did a good video for Tifo recently on it.
Regarding Maddison, he plays better further forward and I don't think he's tactically adaptable like Mount is.
I don't really want either of them, but I think a midfield 3 of Bruno, Casemiro and Mount will work a lot better than with Maddison in there instead of Mount.
I think you're on the money here.
I don't really think Maddison and Mount are massively similar players, honestly. I think people just see two English guys who have both played as attacking midfielders and concluded that they are.
Maddison is far more similar to Bruno than he is Mount, and that's why I think he makes much less sense as a transfer target. Maddison, like Bruno, is a high volume creator. He'll attempt a lot of high-risk moves in a game, and has the technical proficiency to mean that there's a high-reward from it. The issue is that you seldom want more than one of this type of player in your side at any given moment, since you then end up taking too many risks and struggling to exert control over a game.
Mount, in my view, is more of an "advanced 8". I'd say the player in our squad who he's most similar to is Sabitzer. He's technically competent but lacks the proficiency of somebody like Maddison or Bruno to play the "high risk, high reward" style that those two do. His primary strengths lie in the fact that he's exceptionally intelligent off the ball, and this holds true in all phases of the game (attacking, defensive, and transitional). I'm of the opinion that a midfield with Mount in it won't be exceptional without a primary creator alongside him (i.e. Bruno, Maddison etc.), but the work he puts in can really help elevate a midfield that does have one of those players already.
To be honest, with all this said I do have a few doubts over Mount. I don't know if he's comfortable enough under pressure to help us exert control in matches against stronger sides, especially given Casemiro's and Bruno's limitations in that regard. However, I do think he makes considerably more sense than Maddison, who I'd say is essentially just a weaker version of Bruno.