You seem to have a good handle on where the problem is. I am 58, so I grew up with the same “more is better” 1970s fitness ethos that you did… You mention that you know it is a problem but you have not corrected it. It needs to be corrected or you will be following a philosophy that can only result in beating yourself into a hole or being dissatisfied that you didn’t do more… If you have infinite willpower and discipline the best outcome is a state of fatigue where you can only do mediocre workouts and stalled fitness. It is very difficult to see how anyone would want to maintain this for very long so it is more likely that you will get discouraged and quit.
More is not better, it is only more. More intensity today means I can do less tomorow I look at rest, recovery the same way as I look at workouts. If I workout on a recovery day, I FAILED to take a recovery day. If I go hard on an day that was supposed to be easy, I FAILED my easy day. If I go 5hrs when I should have gone 2 hrs, I FAILED to do a two-hour ride that day.
Said another way, there is an optimium amount of training and once you exceed it, you are reducing your fitness. Before you add another workout or push that Z2 workout into Z3, ask yourself “how much fitness and I willing to sacrifice to indulge my desire to hurt more?” It seems unlikely that there many times where riding indoors and reducing your fitness are going to seem worth it if you approach it that way.
Once you correlate your feeling of success with what you cognititivly know to be what you should be doing, it sounds like you will exit the enthusiasm/burnout cycle you describe. Then you will get more results from less input.
If the primary goal is weight loss then you might consider another form of exercise if you want to add more calorie burn. something that doesn’t require recovery Better yet just cut the intake down.