Yes - I am speaking in absolutes in an attempt to simplify to some degree. I do agree maybe 95-99% with everything you say. Obviously impaired recovery from lack of eating properly, lack of sleep, illness, etc. - is an issue. If you lack protein to build a muscle with, it can't magically be created. If you are ill, your body has more immediate stresses that take energy and resources. But, I feel like people often act like if you are overtraining it is because you are under-eating or under-sleeping and that is only half the equation. And the fact is, once you've achieved the necessary diet and sleep routines, doing more won't make any difference. For instance, I have a TDEE of 2800 calories and need 150 g of protein to grow every day. Getting an additional 50 g of protein and 200 calories will NOT make me recover faster because it is more than my body needs. Now if I need 170 and I'm getting 150 - then yes, I will recover faster, but once I've hit my optimal levels, I'm done. Just like if I'm sleeping 10 hours a day, making that 16 hours a day probably won't help....although I'd like to try sometime
As far as the CNS issue - I think the CNS is the big part of it all and the easiest thing to truly over train, I agree there. But I also think that if your muscle fibers aren't recovering, that creates more resources that are necessary to repair, which gets back to the limited resources that your body has (made worse if you aren't even providing the optimal resources through sleep/nutrition/etc.) Again, this is kind of one of those over simplifications - because you can hit a muscle every day and grow. The muscle IS the easier thing to have recover - but I often wonder if it is easier to get your CNS to actually adapt sometimes. However, if you chronically train your muscles and they are just slightly under recovered each time...that builds and eventually those resources will take away from CNS recovery too....
On the other hand, some of this is all good in theory and sometimes you gotta try new things and sometimes theory only gets you so far. I think you and I see pretty much eye to eye on the over-reaching/over-training topic, I was just pointing out the same as you - they are the same thing except over-reaching is planned; and for some reason people don't like the word over-training so no one would do it if it was called "planned over training" but it is all the rage when you call it over-reaching
I think the over-reaching thing is a good way to point out the complexities. There is a difference between chronic and acute stress - and both can lead to adaptations. A small amount of over reaching followed by sufficient recovery/adaptation can be a useful tool, especially in advanced trainees I bet. Sometimes you simply can't "flip the switch" to stimulate adaptation all in one go, especially when the intensities involved preclude certain volumes being used. In other words, someone benching 200 pounds shouldn't need to over-reach as they can train at sufficient intensity with sufficient volume in a single workout to stimulate growth. Someone who is capable of benching 500 pounds, however, will either begin using so much energy for each rep that they cannot do much volume, or they will need to drop weight and use a bunch of volume/frequency. Again, a little simplified.
And your cheat meal analogy is actually pretty dang awesome. I am stealing that and putting it in the library with all the stuff I've stolen from Mentzer. In my eyes, that's a compliment....depending on your thoughts on Mentzer....sorry if it's not...
The final thought here is, I think we pretty much agree on the bulk of everything with such minute twists and angles that it is hard to effectively communicate online and even in a single conversation. I bet if we were training together we would both be learning from those twists....sucks you can't travel over the internet.