There are a few training approaches that are basically different time-in-zone compositions. You're doing what would be called sweet spot training. Another is pyramid training, where you spend a lot of time in zone 2, less in zone 3, and a little in zone 4+. And a third is polarized, where you spend a lot of time in zone 2, none in zone 3, and a little in zone 4+ (which is what you say would be boring). There is some evidence that sweet spot training wears you out without providing a lot of training benefit, although it sounds like you aren't excessively tired by it.

Polarized training is actually fairly popular with pros. Of course, they spend 20+ hours/week on their bikes. It's the approach I'm trying to take with my own training, although I'm not perfectly compliant.