The reason you see a lot of bent solid axles on department store bikes is because they have freewheel hub and they would bend or break hollow axles in the same way because the bearing is so far from the dropout. A bent or broken axle on a quality cassette hub is very rare and thousands of people have been using QR hubs on fully loaded touring bikes without incident for many years.
Crappy QR skewers abound on both dept. store bikes and brand name bikes. Use a good one, like a Shimano XT, and you will never have a problem.
I think you covered the downsides, but the question I would ask is what are the upsides of a solid axle for what you will be using it for? I presume you won't be using a department store brand axle on your bike so the fact that you've seen them bend has no meaning for your considerations. They bend because they are junk and not really made for any serious use.Other than requiring a wrench and taking longer to remove, what is the downside to solid axles?