My first ergo split was a Kimiko (roughly the same as a Sofle v2) which also had this num row I quickly stopped using (I ended up affecting it to F keys, still useless anyway; even for switching VTs I tended to use F keys from one of the layers).
My current daily driver is a 3x6 dactyl with a 4th key under middle and ring finger columns and… a 6 keys (2 rows) thumb clusters. All 6 keys can easily be reached because of the 3D shape. I would say only a couple of keys among the 50 are not really useful, hence it is the sweet spot for me now (for a sculpted keyboard anyway; for a flat one, I have to make it work with smaller thumb clusters).
Anyway the similar layout of the thumb clusters and similar goals (Linux user; typing in French) made me want to comment :).