Dendoncker for me is the exactly the type of profile we need, for the position we find ourselves in. Is he a world class player, no? But he's a very good premier league midfielder.
We need players who have the quality and are ready to play 30+ games in the premier league now.
Players like Happy Gilmour might have higher ceilings (I'm not so sure) but with having such a poor quality squad, and realistically looking like we could get relegated, or the very minimum be involved in a relegation scrap, we don't have the luxury of squandering our limited budget on what if's and maybes.
If Dendoncker has a year left, and is available for 15M, then just get it done, structure it best possible, 5M upfront, 10m over 2/3 years length of contract, and that addresses part of the problem we have, whilst also retaining budget to be used else where.