If that’s what he meant then it’s an execution issue, not an ‘understanding the system’ issue.
Using a nerdy zoological analogy, in a vertebrate and intelligence complexity scale ranging from fish to primates, our system equates to fish.
I'm not trying to get into an argument but I'm pretty sure the offense is way more complicated than you think. Even the seemingly limited playbook they actually use. This isn't pee wee league fb where you go where the play's drawing tells you to go. Take that plus a bunch of read and reactions to D players reactions, blocking and coverage schemes.
I saw a RU offensive playbook from like 25 years ago. I'm drawing a blank on which coach it was. I think it was the guy Walsh from the 49ers stuck us with. That playbook was over 400 pages thick - even simple pass plays had WR reads and reactions, QB reads and reactions, blocking reads - and if they weren't all made correctly the play fails.
Maybe the grey area is I think missed reads is a understanding issue and you think it's a execution issue. To me the execution is the physical move after the read. The actual block, catch, tackle or throw.
If you consider making the read is included in execution then we are only disagreeing about terminology.