the f20 kinda feel like wearing a stiff shell with no liner...especially if wearing a lighter/performance sock.
I picked up a pair of F22 with the expectation they would be slightly softer than my 2009 Malamutes - and holy hell, they seem stiffer compared to my malamutes when they were brand new.
Your post confirms what I suspect regarding the F series boots - still, won't change much, won't pack out, and the padding is not as complete as a boot with a separate liner.
That said, I'm debating between an F3.0 and F4.0 now. I wanted something just a touch softer than the malamute so that when I land jumps (while freeriding) it doesn't punish me the same way the malamutes do. Just a touch of forgiveness would be nice, but nice and stiff to charge hard when I want.