I have the same problem.
Like in this picture from another post we can see big-triangles, but I too always very very small triangles.
Even when I use a value of 0 displacement and use no attributes; put [001] as Basecolor and that is all it still generates many, many small triangles.
ref this post where you can see his landscape has both: Nanite Performance is Not Better than Overdraw Focused LODs [TEST RESULTS]. Epic's Documentation is Dangering Optimization. - #301 by myasga
I also recall from the Captain America/Marvel video it had this as well.
I use world-space coordinates for triplanar mapping so all the textures are at the same tiling/resolution/etc. Is that what drives this?