Have to admit I'm no capologist. You seem to have a good handle on it though. Nightman seems to also.
Nightman and I make efforts to be mythbusters in regards to the cap. It's easier now that Spotrac and OTC can do the calculations for you. Years ago we would post spreadsheets with the what-if calculations for the Cowboys cap scenarios.
Your post was not wrong, but I just wanted to add perspective.
The constant "The Cowboys are in cap Hell" posts that you see are wrong. They were really only in true cap hell one year. In 2013 they had franchised Spencer for the 2nd time and were working on a new contract for Romo. They restructured all contracts to the max including the backup QB which only gained 200K in cap space. The new Romo contract freed up cap space but without his extension, they would not have been able to sign draft picks or a practice squad that year.
In contrast, today they still have the ability to create significant cap space even after using the tag on DLaw. The team is focused on keeping the cap situation clean which is why they avoid big free agent expenditures. Very few teams have "free-agented" their way to the Super Bowl. The Broncos did but most Super Bowl teams were home grown with just a few complimentary free agents.
The Patriots don't put a huge focus on free agents which is part of the reason they don't fall off the map the way the Broncos and other Super Bowl teams have done.
The Giants spent huge money on defensive free agents a couple of years ago but then couldn't afford any offensive linemen. They got good players but they were not a good enough team to justify going for broke at that point.
The Eagles cap is now a mess but they timed it perfectly for their team to peak before the cap ramifications kick in next year. That's a dangerous strategy because if they didn't win they would still have the cap ramifications.
The Patriots model where their cap is more of a straight line on a graph provides a higher probability of winning over the long term than the Eagles model which has high peaks and low valleys on a graph of their cap.
Jerry tried the max spend approach for a long time with poor results but fans still want to go back to that approach.