I'm going through this at the moment with my 16 year old son. Played at a decent EJA standard for a few years, and is now at an academy. They have advised the boys to also get experience in a men's first team, rather than only playing against other academies. He came off his first preseason trial questioning whether he was good enough for mens football, but that experience stood him in good stead for the next trial. Half a season in of playing 90 minutes each week (by a club who have wholeheartedly supported his acclimatisation despite earlier results), he's finally starting to feel comfortable, and is paying the club back. Even though IMO he's the most gifted player in the team, he was nowhere near the physicality and street-smart of the senior players, but he's getting there. Meanwhile his academy football is totally different, technically superior, but without the physical side.
Having seen this, I don't know how any Spurs youth player can get into our team without experiencing senior football at a level they are better than (to take the pressure of needing to impress out of the equation, and also be guaranteed minutes), in order to come back to Spurs and be used to that physicality (to take that part out of the equation of performing in the PL). People talk about Kane's loan spells being unsuccessful, but I bet they were vital to his development.