To each his own. Have you ever tried to bend an action? I have tried to straighten a 700 that was warped from the factory, like most are. Usually the tang is pointing down. Prior to truing it, I tried to straighten it. It was my personal action so I got really aggressive. I never got it to bend at all, and I got far worse on it than any clamp style wrench could think of.
I worry more about twisting it and not being able to get it back to reasonably straight than anything else. I think I might have seen what you are talking about, but it might be something different...the one I had that was tang down seemed more like to me when I dialed it up that it was turned off center or set up out of whack when they machined the outside dimensions. Best I could tell the bolt lug ways were pretty straight, I mean, for a factory Remington. The lug ways were within .002" front to back, but the outside of the receiver was pretty bad, like you could notice it looking at it bad. Like .020" bad. The face was out too. I ground the face perpendicular to the lug ways, lapped the bolt lugs and face and barreled it up...it actually shot pretty good for as bad as the receiver was.
One thing about this receiver, it seemed to be very hard as in Rockwell scale hard.
I have to wonder if the warp is imparted when they broach the lug ways....