From the reasons you described why jumbo didn't work for you, they seem to be clear logical reasons - no indecision, etc. I would say sell it if you don't use it. do not see any reasons described by you that makes keeping something you don't use and don't love. I have all the sizes in classic except maxi. I must admit that I used my jumbos the least. I often wonder if the jumbo is so popular and referenced by many as the "holy grail" simply because most ladies carry around a lot of stuff (lifestyle need or just simply preference). I know I used to. then I realized that all those "just in case" stuff that I tote around all the time in the past had been needed never and perhaps once or twice at the most, and I realized that it's a lot of effort to carry them around for the once that I might need it ever. I think majority of people have problem fitting all the stuff they want / need to carry around inside a M/L size bag so jumbo became a necessary size.
before you buy though, have you tried on a rectangular mini and how do you find it against the square mini, both on how you like the look/shape, where the chains hit your body (shoulder carry vs. cross body), and how stuff you need to carry everyday fit inside both of them? I'm 5' 8" and although I own both, I prefer the rectangular mini, if haven't yet, perhaps try them out in store first?