35 for Sanches?
He's a (physically) strong player for his age. That's really it. He's a strong 18 year old boy. He' not particularly skilled.
There have also been rumors he is not 18 and lately he developed a strange condition in his chest usually associated with performance-enhancing drugs.
It's more because of Jorge Mendes and the relationship with a fund with some big teams in Europe. Basically porto and benfica have, for quite a while, build a relationship with the agent and some shoddy funds to help them finance and sell players. The clubs have audited accounts and they usually just bank between 50-60% of the transfer value. The rest is percentages of third party owners and transfer fees, very shoddy money that seems to be completely untraceable. This ridiculous values are probably just money-laundering.
Sporting had a very incompetent board (luckily they are all about to be legally judged by their decisions).