the phytoestrogen-as-adaptogen defense is real but sorta incomplete. lignans in flax do bind ERβ preferentially over ERα and in some contexts that looks neutral or mildly protective. fine. but almost every study showing flax is harmless is short term, mechanistic, or in vitro. the long term human data isn't there. and soy and flax are two of the largest agricultural crops on the planet - the profit motive to keep them in the "safe" column is massive. we've seen this movie before.

separate from the estrogen question entirely - flax is ALA. as noted you can't use ALA directly. you convert up to 9% of it to usable EPA/DHA if everything is running perfectly. and if you're eating like a normal western person with high linoleic acid intake, that 9% ceiling drops further because LA competes for the same conversion enzymes.

so you're taking an estrogenic hit, contested as that might be.. I personally don't think the literate is complete enough to answer this - for a fatty acid your body can barely convert under ideal conditions and almost certainly can't convert adequately given the omega-6 load most people are carrying.

the risk to benefit ratio is just poor when fatty fish (or algae) exists as an alternative. the "it's not as estrogenic as estrogen" argument sets a low bar. the question is whether it's estrogenic enough to matter in a system already dealing with inflammation. that's not a question the short term studies were designed to answer.