I don't have the DFA 70-210, but I have a DA*60-250, which almost never gets used now that I have the DA 55-300 PLM.
The DA 55-300 PLM plus the 1.4 TC gets you to 420mm. On this image I backed it out a bit to 364mm which improves the IQ. But even in the long end at 420 you can get decent results.
Without the TC full reach works just fine.
It's probable my DA*60-250 is slightly but not significantly better. But despite what's been said, the ease of use is incomparable. How much difference a pound makes depends totally on how long you hold the camera up to your eye, waiting for the perfect pose. I rarely use the DA 55-300 PLM with tripod. With heavier lenses you need the tripod to hold the camera in line with your subject and steady.
If I'd owned the DA 55-300 PLM, I wonder if I would have bought the DA*60-250. It would seem unlikely. ƒ4 is just not that sexy.
Don't get me wrong, the DA*60-250 is no slouch (accept in speed of AF) . DA*60-250 with 1.4 TC at 350mm
The problem for me with the DFA 70-210 would be lack the lack of reach, reach that is necessary in many images.