That's simply wrong. I've seen plenty of people running Primo at pretty low doses together with test (for example 200 Test 200 Primo) and still get their E2 quite a bit lower than usual. It seems to be ratio dependent, i.e. the more the Primo the more of an AI effect you get. Also many people have reported crashing their E2 with ratios like 1:2 or higher. Yeah probably doesn't happen with everybody, but there is plenty of anecdotal evidence of that.
I myself am example of that. Running 100 mg/week Test keeps my E2 around 40 pg/mL. Adding 200 mg/week Primo to that sends my E2 below 10 pg/mL. Confirmed by multiple blood tests. Also my Primo is 100% legit - tested with Jano sending an anonymous sample.