You need an engine in your team. Every great side has one. I think you are getting confused about what an engine is though. A player who can keep play moving, who offers an option all the time and is always there. All the managers you mentioned have it in their side. Its not a player who just goes around kicking things, that would be more of a stopper role.
That's not Gueye though, he doesn't keep play moving at all, in fact, often he slows it right down. For all of his criticism, Mccarthy did/does a better job of keeping play moving, as he rarely took more than 1 touch. Gueye regularly holds onto the ball too long, which is part of the reason he loses it, because he invites pressure and then has to rush his pass. And when he tries playing 1st time, he's one of the worst at it.
I mean, this can't be news to people, he's been doing it for best part of 3 years now, and all the plaudits he receives for his personal stats shouldn't hide from the fact. Same goes for Sigurdsson, the debate between those who use his positive stats and those who are simply underwhelmed by his overall performance is ongoing. It's just being able to see when something doesn't quite fit.
You can forgive the odd below par game, everyone has an off day from time to time, but seeing patterns over time is what causes people to question them.
I have no qualm about Gueye, no reason to not like him, not even to the point of Sigurdsson where I do admittedly hold his transfer fee and weight of expectation against him. And I have no doubt that maybe, in another team, or another system, he may have some use.
But he has never performed a role for Everton whereby even a fraction of the adulation he receives from some is deserved. I genuinely believe so many people were taken in by the early rhetoric around the bargain fee and the stats he achieved being similar to Kantes. The difference being, 1 of them was transforming a relegation threatened team into unlikely champions, while the other was helping a relegation threatened team get relegated.
They are not, and never will be, in the same ballpark, and his value is overestimated because of the supposed similarities. If we can get anything over £20m for him, we would be fools not to.