You’ve got it!! The more base you have the better. Think of it as a bank account. The more money in that bank account the more you can do with it before you find yourself out of money. At some point the pure volume approach of low intensity training will need to be supplemented with some additional higher intensity work so that the higher power muscle fibers also begin to get an aerobic training effect. As you will see when reading TftNA the high intensity work is not a replacement for, but is rather, a supplement to, the basic aerobic work used to elevate your aerobic threshold.
If you find yourself stagnating in aerobic progression then it will be time to add some Z3 or Z4 workouts 1x/week.
I hope this helps.