Hard to know how any young player is going to turn out but no way is Tel in the 50/60 million bracket , just posturing by Bayern or his agent.
Look how a young De Bruyne turned out , signed at 20 yrs old by Chelski , played just three games sent out on loan and eventually sold , didn't turn out a bad young player did he.
Don't think KDB had 60 games in league for Bayern, 13 games for a PL, plus 23 European cup appearances (including 15+ in CL) at 20. Tel is a prospect, he played/scored for Bayern at 17.
I actually don't think we as Spurs fans can judge him very well, he came into a massively struggling Spurs side when he was in his first form downturn of his career and had had limited playing time in 6 months prior to joining us. Seems like the club saw something in training, previous performances that indicate we are confident there is a player there.