i do not agree with - at least for the Blue Angels. T-birds -- don't know. I would find it odd that something that is unfit for military operations would be fit for (extreme) aerobatic flight, high G-loads, etc. would be placed into service with the demonstration team(s) from either the AF or Navy. Since only an insider would know what the exact problems experienced with the two aircraft during the show I was at - all we can do is guess.
There is unfit and there is unfit. It is not unusual for older aircraft to be mechanically fine but not up to date on the latest software loads or upgrades. You may not want to take the aircraft that is not most current into combat, but there is nothing unsafe about flying it in training or exhibition.
The F-18 (and pretty much all current aircraft) undergoes constant upgrades after delivery. The software is regularly updated, and hardware somewhat less frequently. Some software loads apply only to certain hardware configured aircraft. Unless there are safety of flight issues addressed in a software load, if it is primarily capabilities oriented, it would not surprise me if the BA birds did not get such loads, or hardware updates. Possibly, just guessing here as I have nothing concrete to back this up, the BAs may indeed be flying aircraft that active squadrons may not want, aircraft that might incur significant cost to bring up to date. No reason to spend that money if the current configuration works fine for the BAs purposes.
T!