I think you overstate Celtic's importance, and diminish Everton (and the Prem's) ability to get players.
Celtic have sold their best players to Southampton more than once. Celtic don't have pull. The report was that the fee was agreed with the agent in this instance. He's on 15k, and it said we offered a starting wage of 85k. That's over a 400% wage increase, to play at a better level that will improve you more.
It'll be about the fees between the two clubs.
Its possibly my heart talking lad. But I'm not the only person who has said in this thread that if you watch his interviews, it doesn't at all look like he is desperate to leave.
But Stuart Armstrong leaving Celtic for Southampton who can easily be replaced by John McGinn is a world away from KT leaving. For reasons you did/didnt mention.
Takeaway > The lad doesn't feel he needs to leave. Yet.
I've heard a lot about how we 'develop young players' over the years or about this 'new leadership structure' being a step forward. Yet as discussed we haggle over £3m. Kind of reminds me of the day of Peter Johnson not letting Joe Royle have a few quid more for Tore Andre Flo or CLiff FInch (same act) for Dion Dublin who Kendall wanted to sign.
I know you say its the club but I really do knowing it think the player either thinks he has better options or would do better elsewhere. So I'm becoming a little worried how young players are viewing Everton as a place to develop at the moment. See Lookman as a fine example.