That has always been the case and probably always will be, nobody was more cautious than SAF with transfers, often wanting to see potential targets at a higher level first(Ferdinand, Berbatov, Veron et al)and ending up paying double or triple what they'd have cost if he'd gambled on them earlier - but that probably applies to all the big clubs to some extent.
And yeah Tielemans great talent, but do you not think all the big clubs in Europe ourselves included would have been aware of him since he was 15/16 and yet when he did move from Belgium he ended up in France where he by all accounts didn't pull up any trees, and he's now at a club who think(despite their recent Premier League win) it's an achievement to finish in the top 10.
Sorry you are a bit confused here. Do you need scouts to tell you to buy a 100m player? Or a 70m? or a 50m?
You need scouts to identify a 16-20 player costing probably around 10-20m, and we get rip off for a bit paying 20-30m. Veron, Berbatov and Ferdinard for that matter, didn't fit into this category.
Only Rafael twins, Hernandez, fit into the scouting territory. OK if you add Tosic, Bebe, Obertan, Djouf - who was the guy from Celtic, and another from Championship, who hardly had a game?
Park was already an established player, same for Zaha, Depay, Darmian, Blind, Rojo. Scouts might tip you off but there are enough opportunity for the managers to see for himself.