*shrug*

IIRC I made two full pulls with cores. I got 1 5*. (on first of the two pulls)

I've gotten 0 5* from my 4 factory slots in all the time I've been playing.
-however-
I'm currently sitting on 2 and a half 5* tanks worth of blueprints, a significant number of which have come from recycling junk gotten via those factories.

So I disagree that factories are better than pulls to get a 5* "straight out". However, they are better than pulls to get blueprints, which can be used to get certain 5*'s. (Reason I have so many blueprints is so far since I got 3k there hasn't been a 5* tank available via research I want/need.)