After we missed out on De Jong, we allegedly looked at Rabiot and ended up with Casemiro. The fact we didn't end up with a similar profile of player has less to do with how rare they are and more to do with the fact that, obviously, our recruitment team had not identified a profile of player they wanted.
For the umpteenth summer in a row we ended the window scrambling about looking for the best available instead of working to a plan.
If your point is that very few players can do the job to the same standard as De Jong, well then I agree with you. However, it's certainly not De Jong or bust. There are plenty of players who are competent at receiving the ball from the back four, turning and moving up the field.
You are right to say that there's always a risk when buying from abroad. But that risk would exist for De Jong as much as it might have existed for players like Enzo Le Fee. There were other options we could have looked at that offer similar characteristics. De Jong is not so unique that if we couldn't get him we should have just abandoned looking for that sort of player and just get the biggest name we can in classic United style.
We turned Rabiot down due to excessive wage demands (or they turned us down due to not paying them what they wanted, if you prefer to see it that way). Would you want us to keep going the way of paying players upwards of £300k/w like we do with Sancho just because that's the only way to get them through the door here?
Either you subscribe to the theory that EtH decides all the transfers or you don't. So if you believe that EtH decides all the targets then going from Frenkie to Casemiro signals that EtH went "I can't get a player with the skillset that I want so I'll have to do something else tactically and adapt to not having that player", considering his familiarity with FdJ. Casemiro was in the works for many months before he actually signed so I doubt the part about us scrambling, but rather pulling the trigger on something that was already set in motion.
On the other hand, if EtH had no say and the footballing structure decided to go from Frenkie to Casemiro then obviously they went for big names only and couldn't have considered the profile of the player considering their differences, and I have a hard time thinking that considering they wanted a clean break from the Woodward era. If we'd ended that summer with Enzo Le Fee, who you refer to, as our second midfield signing next to Eriksen, what would the reaction on here have been? And what would the verdict have been had we not qualified for the CL this season?
So yes, my point is that very few players can do what de Jong does, and even those who fit the bill if you're just looking at the statistical profile (like Amrabat) aren't certain to be successful, which is why the constant clamour on here for lesser-known players is such a pointless thing, because those opinions are always stated with absolute certainty, yet can never be proven one way or the other (except for Amrabat).
You refer to Enzo Le Fee, but there have been tons of players who have been the solution to our midfield issues who haven't amounted to much or secured moves to big clubs. It's not like we as a club, when we lost Carrick and Scholes, went "nah we don't want those type of players anymore". They're rare and even if the footballing structure finds them due to searching for their profile it might not be as simple as just going and getting them. We were interested in Enzo Fernandez when he moved to Benfica, but who's to say that we would've been successful with that if we'd really pushed for it? We couldn't get Bellingham due to not offering first-team football at the time. When we came in for Caicedo a third-party ownership problem arose which might have had to do with the profile of our club with people inserting themselves into the deal which they weren't interested in doing when Brighton came calling. They're obviously not the same style of players, but I can understand that a manager who is open to adapting his team's style based on available players going in a different direction when a player that has a style essential to one tactical approach isn't available.
That is what we've done since not getting FdJ, in going for the 4-1-4-1 and signing Mount instead of spending £20m each on three or four mini-de Jongs in the hope that one will be decent. Whether that was a good decision remains to be seen, but I can understand the thinking and I don't subscribe to the notion that getting another player like FdJ was feasible at the time, and the Amrabat signing has showed that having a statistical profile that shows that you're good at progressive carries and passes isn't a guarantee that you can do the job that FdJ was supposed to do.