My post on page one had nothing to do with flex or concentricity.
As was pointed out ALL presses have some in common. Progressives, even Dillons flex too....and you have to be careful to fully "populate" a tool head or you get more "tilt" than you want. I doubt any of the turrets are bad presses. The RCBS is lighter than green and orange giants, and the Lee is a bit light too, but at least the Lee seems to be supported around the perimeter to help make up for it. That said, all of them work well enough to make good ammo.
My objection to turrets is the work. Same work as a single....but maybe a little faster to the next operation. But then Lee and Hornady have quick change die systems that work too. That said, how hard it it really, to unscrew and screw in a die that's already set with a set screw nut. For me it was the # of handle strokes and my tireder body, that made me buy progressives....flex had nothing to do with it.
Flex and concentricity has been worked around pretty effectively for 50 years...longer for others. I remember back when I started with a brand new Rock Chucker I, that I was told to loosen the shell holder spring so it could move and center itself, so the press stroke could line up the case with the die, and not to hurry the stroke and force it into it such that it changed the geometry of the case.