I can definitely agree with the points here. I think it just boils down to the unfortunate fact that WaniKani uses fixed intervals and further has intervals stop at around 5-6 months of initially seeing the word. So we never really get to stretch the legs of long term retention.
Regarding when to add lessons, I used to use Lesson Lock before they added fixed lessons. But I still appreciate the feature of locking reviews until the apprentice items fall below a specified number. So I might recommend that and finding a nice number that makes zeroing out reviews doable.
However, I also agree with there not being a great importance on having a large vocabulary only from brute forcing SRS. While I personally prefer doing it that way (and I don’t really recommend it due to workload issues), at a certain point, most of your exposure should come from immersion anyway and any words that aren’t repeated in your immersion are basically not realistically relevant to you and therefore can spare a dictionary check whenever you do encounter it, if at all.