I really don't know why flushing is controversial. Logically, if you don't want deficiencies then you provide inputs in abundance. There is no 'feeding the plant perfectly the exact amount it will uptake' without sheer coincidence, and it would be as repeatable as winning the PowerBall.
There was this big push a few years ago by some bro-podcasters and grow-bro-youtubers...with the argument that 'we dont flush other crops so why would we flush cannabis'. I find that argument about as sound as silence. We don't smoke tomatoes. Further, if you use living soil and then don't flush at all - I can taste the worm juice and bat feces in your crop. Straight up, I can. Also, your ash is not white and floating away.
Nobody who tells you flushing is a myth has a quantitative reason for this. There are some growers and breeders that have my full respect in every way, but I wouldn't touch their flower crop with a 10 foot pole, just because of the lack of a flush. I guess if you are used to street flower (likely cartel derived with insane pesticides and more and no flushing) then you probably think your unflushed flower tastes great. The ceiling goes higher though.
My flushing has the purpose of cutting off any further nutrient uptake, forcing her to dig inter her foliage to burn down. All in an effort to have less sugars, less salts, less chlorophyll going into my dry/cure.
Regardless of which influencer you hop behind in that argument, why provide nutrients to this plant when she is clearly approaching harvest? Wasteful/inefficient at best.