There has been a lot of research around weight and COVID. Even among the vaccinated, I believe that their is a difference in efficacy based on those who are healthy and those who are overweight and those that have underlying issues (because some treat them independently).
The other numbers that don't lie is the fact that majority of the unvaccinated being hospitalized are the obese (which we know also leads to other underlying issues). There is plenty of research showing the correlation of the overweight and COVID (and truthfully, most other diseases, as many who are overweight also have weakened immune systems) and this was early into COVID.
Just making it about "the unvaccinated" disregards all other data out there detailing the specifics. For severe symptoms, COVID looks to be pretty discriminate and obesity and underlying issues seems to be the main drivers.