I think most people grab the whole tank, rather than the lever alone doing the lift, so the extra weight should probably not be an issue. For the record, the last ten years I have used a volume of 260ml.
There are two issues here. The first is how much solution is needed to assure appropriate flow patterns within the drum and even development. I'd guess that that's the criterion used by Jobo in specifying 210ml as the minimum volume. But the second question is how much solution is needed to have an adequate amount of developing agent for the amount of film that's loaded in the tank. That will vary, depending on the developer and dilution being used. There are developer/dilution combinations for which 210ml would be inadequate. Check the documentation for your developer to see how its capacity is defined.