Bayern will obviously have better chances of signing players from other Bundesliga teams mainly because many players are settled in the Bundesliga and many have families settled there. It is similar in the EPL. If a young non-English player plying his trade in the EPL for a while is available, United will have a better chance of getting him than Bayern. Does not prove that United will have a bigger pull than Bayern.
Anyway, it is difficult to prove either way. But Real and Barca are special cases and then Bayern and United are at a similar playing level.
Madrid were only a special case since the turn of the millennium, even then their specialness consisted of spending obscene amounts of money on players that no other side would match.
Who were Barca pre Ronaldinho? Where were all the players clammering to play for them?
They were big sides and all, but this reputation for being the destination that all players strive to play for is a modern notion that will soon end.
It won't last because it can't last. Look at Madrid. From signing the likes of Zidane and Ronaldo they are now signing their stars from The likes of Spurs / Monaco / Bremen / Lyon / Celta Vigo / Porto etc. The step up clubs. Yet they still have this reputation as a club who takes any player they want regardless of who they play for.
There are players like DDG but that has personal complications that sets it apart but It's not as if they're walking in and saying we will have Hazard / Pogba / Muller / Vidal and name your price.
How many big money established players have they signed from other major clubs that they're stolen away? Kross?
The lustre of their pre Ronaldo era shone a little less due to the English and Barca domination. They come into prominence yet again when the English are at their lowest ebb.
My theory for that is the Premiership doesn't necessarily sign the best in the world. Our sides won't go out and sign Naymar from Barca for example. Our sides would be the clubs rivalling Madrid for the James or Varanes, the players who are ready to reach that top tier.
The English have been atrocious in this regard which has held us back and allowed Madrid to have the market to themselves. It's not as if I'm saying United will stop this single handedly, but it's the English top 4. Not only is it 4 other rivals for the signature, it's rivals that can pick them up earlier with more guarentees than Madrid could offer.
There's examples of our sides dropping the ball. Varane was ours until we confused him with the Jones signing. Modric belonged to Chelsea until Levy interfered. Suarez was Arsenal bound before they refused to honour the buy out clause. United turned down James when he was on trial. Bale was ours until he was guarenteed game time at Spurs.
That's Madrid inadvertently profiting off inexplicable sloppiness. Would they have persued these players if they already made the step up like they have or would they have looked elsewhere, for example would Herrera be a Madrid player right now if Modric opted for Chelsea? Would they have signed Silva if Bayern wanted Ozil?
Yet in these instances, whoever they did sign would be paraded as the best in their position and always getting who they wanted.