This is an age old coaching debate. How much of an advantage do you get by adding complexity to an offensive or defensive scheme vs how much of an advantage do you gain by simplifying a scheme so players can "play fast".
I went through the same thing over 50 years ago at the HS level, when you had 60 odd kids (some of whom have never played before) and 4 or 5 coaches and had 3 weeks to get ready for an entire season and no spring football, AND its a part time job. Imagine when you have a dozen or more coaches and another dozen or so support staff, PLUS an unlimited amount of time. So YEAH, it would be very easy to create very complex schemes, routes and plays that would seemingly give that scheme advantages.
Obviously if your team is able to absorb all the complexity you have your advantage. However if you slip just a bit too much, then you risk creating execution flaws. Plus the fact is that not all athletes process what they see at the same rate. It doesn't make them stupid, its just how they are wired.
I don't think you can compare high school football to pro football. When you enter the NFL you are now doing this for a JOB not as a hobby.
These are now MEN who have finished college or are now out of college having flashed enough tools to indicate that they are legitimate pro prospects. There is and should be a huge difference in ability and mindset comparing adult pro athletes to kids in their teens who are doing football mostly for fun.
From the comments of past players, it's obvious that the Patriots have one of the tougher playbooks in the league. But so what? In the end it's still football and not rocket science.
If you watch this video, BOB breaks down some of the concepts the Patriots exploit in their option routes:
You can start to understand what they are looking for. They are trying to find, exploit, and create favorable matchups. The most 'brain processing' is demanded from the QB position. The WR just needs to be where the QB expects him to be based on the read, and then they should be able to find an opening or mismatch in the defense if the route concept the play called for works.
During the week, the team will get what, dozens of snaps practicing those concepts? Over the course of the season, hundreds of snaps? Add film study, team meetings, and your own personal study for those motivated enough to perfect their craft. This is the stuff that you EXPECT your dedicated professional who does this JOB for a living to get down.
I get it some guys aren't suited for the Patriots style offense. But it's not rocket science. Football requires football IQ, which is a different thing than academic IQ where you stuff your nose in a book and memorize complicated math fomulas. Some football players can create dynamic situations on the field due to their pure talent in the moment, but every playcall expects players to at least know how to get into the position that the QB expects them to be in so they get the opportunity to make the play if the defense at that time gives them that chance.
Simplify the language of the play calls, cool. That's fine. The Patriots are reportedly doing that this year. That probably helps the players do their job a little easier. But if you don't get the playbook, it's on you, the player, not the system imo. Study HARDER. Put in the extra hours to know your assignment, learn how to read a defense, learn where the QB wants you to be. If you're not sure, ask the QB, hey on this play, if I read this, where would you like me to be? They work in the SAME building, it's not like you can't communicate with him, in fact I'm sure the QB would appreciate it if the WR approached him and asked him these questions.
A complex system is not a suitable EXCUSE for a professional football player not to DO their damn job! So stop making excuses. Wide receivers like N'Keal Harry didn't fail because of the system, they failed because they didn't GIT GUD for their damn job!