Does heavy withdrawal bleeding also indicate not pregnant?

I recently read that some don't believe withdrawal bleeding, or birth control periods, can tell you if you're not pregnant like a regular period can. So you could have this bleeding for months and not realize you're pregnant.

HOWEVER, I also researched that you would definitely stop bleeding because the drop in hormones during your placebo week onsets withdrawal bleeding. If your hormones did not drop (aka, pregnancy) then you wouldn't have this withdrawal bleeding.

***this is specifically heavy, bright red, filling pads/tamps over days bleeding not light pink or brown light bleeding***

I think the second theory is more probable. What about y'all?