Definitely a risk of getting stale, both physically and mentally, if you keep on doing Base/Build without a proper break or without a taper to have some fun actually using that fitness when you’re fresh.
Approach I tend to do is just have a period where I’m still riding nearly every day but completely unstructured and just for fun. Normally ends up being 1-2 weeks where I ride pretty short and easy, and then as the freshness comes back I end up doing something similar to traditional base training with some long z2-3 rides. I find that even if those weeks are pretty high TSS, then the mental freedom of not having any kind of plan or structure, plus the relatively low intensity of keeping it nearly all below sweet spot, is enough that when I get back into structure I’m pretty fresh but having lost little or no fitness.