Well, for a 17yo? He doesn't has a future secured, I don't think any club would pay much more for him.
How many u17 WC winners have turned out bad? Some have turned out good, of course, but it's a big risk to put much more money on such a young boy.
Thats a very poor judgement of the situation.
Anderlecht can pay reasonable wages considering its a belgian team.
They have championsleague group stages, and Tielemans is a key player who'll play all 6 games.
Anderlecht have a history of keeping very promising players, and selling them after 3-4 years for significant numbers.
You see it the wrong way. "clubs wouldnt pay much for him". You have the assumption it depends on the buyer.
But anderlecht isnt a team that wants to sell him. Why would they accept 7 mil for a player that they dont want to sell.
Its allways the seller. If the seller doesnt want to sell they can perfectly say "pay us 25 mil of get the fuck out".