I would have to disagree with that. United have had to pay good chunk of money to get players mediocre players from outside their league like Bailley, Lindelof, Depay, Mkhitaryan for high wages. If they want to buy any decent PL player, they end up spending as much as (and frequently more than) BM's erstwhile record transfer (41 Mil euros until 2019) for squad players like - Mata, Fellaini, Shaw, Matic.
But now you're arguing in hindsight about who United bought, and the prices paid, which I think is a very different question than who they have access to or rather who they could be buying. Are players in England more expensive? Yeah, but you're comparing players that were bought to hopefully improve the first eleven at some point, with players that Bayern brought in as squad options like Rode or Rudy.. In many transfer dealings Bayern has had the good fortune that in most positions they already have exceptional players, so players they sign don't always have to replace the established player (immediately). For the most part United haven't really had that many completely undisputed players in a lot of positions for a long time. Hence you see fewer signings that are obviously squad options from the start.
The fact that many of United's signings fail to deliver doesn't mean that mediocre players cost a fortune necessarily, it just means that the players they
have bought turned out mediocre for whatever reason. None of the players you listed there were brought in under the expectation that they weren't good players, or even as squad options. Someone like Daniel James, or Telles fit that description better. Bayern are penny pinchers a lot of the time, so a lot of players they would probably like to have are immediately out of the question, even players like Dest for instance. That being said, nothing is stopping United from buying the players Bayern bought cheaply. They won't magically be twice as expensive. Bayern buys the players they do, because those are the ones affordable to them, in the same way that Juventus for instance frequently target free agent players. Some players may end up preferring Bayern, but you rarely read about United being interested in the same players as them.
From the list of players you had mentioned earlier, there isn't many players I see that wouldn't have been possible for United. I do see players that United would never be interested in in the first place, but that's a different matter.
Agree with this apart from that Gomez was a 40 goal striker at the start of the last decade for them. He was poor at building up play, but was lethal in the penalty area. Agreed, that these players were never lynchpins for BM, but the fact is they were more than good for rest of the BL, and you need these sort of players if want to compete on all fronts throughout the season.
Yeah Gomez is a very underrated player, but a bit unfortunate always in the way that strikers can be the face of failure without necessarily being the cause; that final against Chelsea for instance. I kind of excluded him because his time at the club was already coming to an end by the time Bayern became so dominant. His best seasons were when Dortmund won the title.
As you say, they've failed in a lot of their international transfers, so how are they still on that crazy BL winning streak? They have poor transfers (generally outside their league) like most other clubs. In a highly competitive league like the PL, poor buys lead you to miss CL, while for BM the worst case scenario generally is a second place finish. My reading is that the baseline level for BM is the same as the best for most of the BL, when you add in world class talent outside the league, you have a team way above their competition and competent against European teams. If the BL baseline falls, then BM baseline would also be expected to fall, since those are the bread and butter players for BM.
Where did I say they failed a lot of international transfers? I don't think that's really the case. They've had their share of duds, but overall I think they've done pretty well with international transfers. Even with the ones that didn't succeed, Bayern have had such continuity in their team that compensated for players that didn't perform. That's down to having fantastic coaches in that time frame, but also the unexpected longevity of some players. Players brought in to replace Ribery and Robben for instance failed to do so, but it didn't matter because they just kept going at such a high level.
I'm not sure I follow you on the whole baseline thing, but if you're saying that Bayern's level would decrease if their domestic league stops producing talent, then I'd argue that the same applies to anywhere really. As for poor transfers leading to missing the CL in the PL.. not sure I agree, if you already have a good team to begin with. The inverse of that would be, that a team relies on good transfers to make top 4, which wouldn't really be as necessary if that club already had a very good team? And that's generally been the case for Bayern. I can't see a single season in which Bayern wouldn't have made the CL in the Premier League in the past decade.