That is a good point. It is often said that "OK, his coaching is not up to standard required at Manchester United, but his transfers were good". The problem is that his transfer record is actually quite hit and miss.
For me to call a transfer policy successfull it has to include up-and-coming players that were bought for a reasonable price - which in hindsight seems super cheap - and developed into key first-teamers. Mane, Salah, Robertson etc were not sure things at the time Liverpool bought them, but now the prices they paid look like a bargain, since they developed so well (here again the quality of coaching plays a role). Zidane's RM side - Marcelo, Ramos, Varane, Casemiro, Benzema - same. Fergie's 06-08 side - Vidic, Evra, Carrick, Ronaldo were not expensive even at that time, and even the more expensive ones - Rooney and Rio looked great value for money in the end. All of those players were easily worth a lot more (or even multiple times their transfer fee) after a couple of years at the new club.
With Ole - let's look at his first - much lauded -transfer window. We did well to sell James at a profit, but he failed to establish himself as a first teamer. We are still discussing if 50m AWB is good enough. And whilst Maguire is a good player - he cost more than VVD and we would struggle to recoup his money if we wanted.
At the same time, as you correctly pointed out, Ole splashed close to 150m on VdB, Amad and Sancho, two of whom are fringe players still, and one has not had a great start (but of course to early to judge). We bought several experienced players without paying a fortune (Cavani, Ronaldo, Varane), but it hardly takes a genius to identify them. And most importantly - there was not a single transfer like I listed before - up-and-coming player who develops and establishes himself as first teamer so that his transfer fee looks very cheap in hindsight. No great team was built by buying the entire first 11 for big money/wages (although City/PSG come close, but they still have some key players that were young and relatively cheap when they bought them).
So in sum, whereas I would not say that Ole's transfers have been bad or disastrous, I would merely say that his transfer policy has been OK/decent but he does not deserve huge praise for it.