I think Spurs do have good young players that Pochettino will be right to place his faith in. Alli and Pritchard both have the potential to be really good players and England squad regulars. Two very promising youngsters.
The difference between Alli/Pritchard and Mason/Bentaleb is I don't think the latter two have that potential to become top players. I think Mason and Bentaleb will always be good but not great Premier League players, so it seems a little strange to place so much faith in two young players who don't have too much potential. Alli and Pritchard in 3/4 years could both be fantastic players, could Mason and Bentaleb? I don't think so, they're more likely to be at Sunderland than Man City.
Dier is a really good young centre back, but he's playing out of position in centre midfield and it shows. If Spurs needed a holding midfielder, why not sign one? Cabaye and Wanyama would have solved your centre midfielder problem for around £30 million.