This is definitively not true. There have been alot of top BL players we weren't able to buy, see Reus (prefered Dortmund), Sané/KDB (snapped up by City), Vidal when he went to Juve (Völler didn't want to sell to us), Diego Ribas (Bremen also didn't want to sell). The last top players we bought from the BL were Lewa, Hummels (wanted to go to us) and Götze (release clause). That's comparable to Sanchez/RVP going to you guys for example. If we wanted a top BL prospect like Bailey/Werner/Pulisic, we'd have to pay (at least) the same price that other clubs would (see Sané/KDB), unless the player himself explicitly wants to go to us (and even then it doesn't work, Vidal promised to go to us but left for Juve the first time).