It doesn't help that people insist on rating a buy before they have even kicked a ball, ultimately you can't rate a purchase until much further down the line, and in full really not until their spell at Spurs is over, and then you can also take into account return on investment and such things.
Take VDV as a case study, time of purchase not viewed as a top buy, 10 games in all of a sudden many would call him a top buy, ff 6 months and maybe he's not fully right following injury, maybe his form has dipped, ff 3 years maybe he never got back to his initial level and has been loaned out and then sold at a loss, maybe he came back stronger and got an £80m move to Madrid...
Only at the end can you say who was a top buy or not.