When did I say that?
I see them and I think if I could sign now a player for Madrid would be Alli because I think he is already established(and of course he has to prove and improve) and simply because I like him.
I don´t imagine him suddenly disappearing and becoming a player with a medium low profile however I have doubts about the others. Dembele,Asensio,Rashford,Martial,Sane...
I do not see any of them entrenched in the elite.
If the picture was the opposite, Alli at United and Rashford / Martial at Tottenham , the opinions would be the same?
Fair enough, it seems like you simply have a personal preference for Alli which is completely fine and understandable.
When you said that those attackers have a lot to prove and didn't mention the same for Alli, I guess it came across as strange to me. However, if you were to rate Alli's potential as higher than Rashford's/Martial's/Dembele's, I would be interested to find out what that rating is based on. I know you didn't say that, but if you do think that, it would be something interesting to discuss.
I think all four of those players have shown tremendous ability last season, as their first real season at the very top level and all four seem like they may be able to continue that form, at least certainly Rashford and Dembele have shown it so far this season as well.
To answer your question: If I was a United fan and we had Alli, and Spurs had both Rashford and Martial, I would honestly be extremely jealous and would swap them in a nano-second. Just like how I'm currently very envious of Dortmund for having Dembele and Weigl and rate both of these players above all of United's current options in their respective positions.
So really it's not about bias, I simply consider these players to be absolutely elite young talents and although everything is possible, it would be very difficult to imagine most of them not developing into world-class players.
It's often said that when talking about young players, it's almost pointless to discuss how they'll turn out because there are way too many factors that may affect their development and this breeds somewhat of a cynicism towards them. An example of this is our Reserve/Youth forum. Many good/excellent talents in our academy are constantly rated lower by posters than their true ability reflects, and I believe that has to do with the disappointments of previous experiences with players such as Macheda, Adnan, Anderson and others.
However, when you reach this top, elite level of young talent that we're discussing here, it tends to be more of a sure thing that they'll develop as expected. As an exercise, we can look at the list of previous winners of the Golden Boy award. Only Anderson, Pato and Balotelli have really disappointed. The rest, we can safely say have been world-class players at one point or the other; the likes of Rooney, Fabregas, Aguero, Isco, Gotze, Messi and Pogba.
So I do believe there's a very good chance that players such as Martial, Dembele, Rashford, etc. will develop as well as expected. Of course, a lot depends on mentality and temperament.
Sorry, I have been rambling on and on in this post, but I have always found this topic very interesting and it's exciting to discuss these players, I really do believe they are extremely special talents.