The whole argument began from a fallacy, i'm surprised nobody mentioned it
Who exactly tried to sign Eriksen from Spurs last summer? Kane? Alli? Over the last 5 years, only two spurs players became a real transfer target for a european heavyweight. They sold both. Spurs superior ability to retain players right now is virtual. We have no way to know whether spurs can keep hold of eriksen until a real madrid/barcelona tries to sign him. Dortmund sold players to bigger teams that offered them much bigger wages. In the case of Hummels, they sold him with one year left on his contract after 8 years of service. Reus - local guy - had literally all of europe after him and choose to stay at dortmund
Spurs biggest advantage with Kane and Alli is that they are both british, one of them from their academy, the other is 20 years old in his second season, still too early for the mega-clubs to move for him.