You have very rational points, but thats not how Zach is painting it tho is it? They still managed to attract said players at the end of the day.
Moves are all about timing and needs, everyone could used Pogba like they could use Verratti, with the addes bonus of Pogba being a super star that can become a huge brand name. But with the timing of that point and how much he would cost, how many teams he were willing go to besides Man U were ready to pay up? That only leaves Barca and Real, former were kinda strapped and lost in their dealings even if he was affordable to them (Gomes, Alcaer and Suarez cost over 100m, all duds) while Real dont have practical need for a top midfielder.
The wish and preference of the player matters too, Pogba wanted Man U and is probably most attached to EPL of all the leagues, he didnt care for best possible chance to win CL by this choice. Verratti has more options if he leaves and specfically would move to improve his chance to win something other then league title (read: CL) but also depends entirely on what he cost when it comes to his options. However unlikely scenario it is, if push comes to shove and Barca or Real baulk at PSGs price and dont want to commit, and newly CL ready Man U wants to bid record sum, yeah you bet they would be a viable option for him. Not the smartest option but a viable one. At some point he will tire of doing the same thing in PSG for 5 years (kinda like how Pogba did for us). They would be low in the totem pole of his choices due to CL and probably not being his type of football, but still there due to how big the club is (PSG are nothing in comparison and he still went there).
People forget too quickly they are by far the biggiest English club since their closest historical rival Liverpool been a meandering joke for near 3 decades. Dumbassess that have more money then sense and been faltering for far too long, but they can simply afford these mistakes and they are one great coach or competent management away from bouncing back with some consistency to the elite. Too big of a club to keep failing too long.
And regarding rest of your question, Di Maria was defenitely a star, injury plagued by Falcao was too. But besides that, yeah if your options are Barca, Real, Bayern or even neighbouring city at the time, you would not pick Man U.