Pogba, a highly promising 18 yo youngster at Manchester United, was on the outside looking in with Carrick, Scholes, Anderson, and company for a premier team in England and Europe. Alli, a promising midfielder from the 'lower leagues' and now player for a better than average team, has never faced the same pressure or adversity as Pogba at the same age. Alli would never have gotten into the same Manchester United team.
I think the comparisons are silly. Pogba, before his 21st birthday, has played for two of the very best teams in their respective countries and has won titles, the FIFA U20 Golden Ball, Golden boy, FIFA young player of the year award, and started in the EUFA Champions League. He's probably the most sought after midfielder in the world at 22. If Manchester United were in a similar position as Tottenham he would most likely would have played more.
On the other hand, Alli may win the Barclay's young player of the year award for a team with aspirations of making it into Europe and has a strong chance of making this summer's Euro 2016 team.
I hope this puts things into perspective.