Have you seen the absolute nail biters Ajax have had in their second legs after taking healthy leads into them? Where does that fall into their tactical brilliance?
Not, I didn't claim they have tactical omnipotence. They are not good at defending a lead, so they will try to extend the lead. If you're good at attacking, conceding a goal isn't that much of a problem. They're convinced that they can make more goals than the opposition because they play better football. They are frail, but I don't think United is the most likely team to exploit that, and with young players that experience a season like this, they become less vulnerable with every big game. United had two nailbiters too, so how big is that difference? How is a 2-0 home win a more comfortable lead for an attacking team than a 0-1 away win for a defensive team?
I agree with the gist of your original post but the comments about the Ajax tea lady having more positional awareness than Pogba and your stating that we "always play bad" is what got you the reactions you're getting.
There is a way to put your point across without going into daft, tactless hyperbole.
I used a hyperbole to get a point across. Their attacking style of play with the emphasis on the positional game and awareness dates back to the sixties. It has evolved an been tweaked and managers have been playing it differently, but it's deep down in the clubs DNA to the extend that the tea lady and the laundry lady know a lot about it. For example 17-year old Kluivert is ahead of 23-year old Younes when it comes to positioning and awareness because Younes has only been two years at Ajax and German football wasn't much of a preparation.
On top of that, Bosz has been working on his version, his interpretation of Ajax-football from august and that was a steep learning curve, losing them the league title early in the season. But they play very well now, you can play very well with limited players and play poorly with excellent players. You can gain a huge advantage over a team of better players by playing more as a team, gel better and be much more fluent. Mourinho didn't work on that since august, and there's no way he could make up for that in 10 days. United could play relatively well as a team compared to earlier matches, but not to the extend Ajax does because that's a full season's work on top of half a century of 'philosophy'. If that wasn't the case, Ajax wouldn't have made it to the final and Ajax wouldn't pose a threat to United at all.
So it's not about the quality of individual Ajax-players, the problem United has to solve is that the Ajax players will be a step ahead because they know where to move earlier.