Two of my relatives in their 80's just got it without any vaccine and similarly had a nasty flu; they took ivermectin and didn't need any urgent treatment, although O2 levels did drop into the low 90's at times. About five days after diagnosis (and well after the worst days), they received monoclonals. They're still weak but recovering. I know another person (young, in 20's) who had similar symptoms -- brutal flu, similarly believed that ivermectin "saved" him. Of course, it's unknown (but
https://www.wsj.com/articles/fda-ivermectin-covid-19-coronav... )
Most cases seem to be relatively mild. There are always the ones that aren't, though, but it does seem like (in the absence of real, double-blind, public data) the vaccine doesn't have too much of an impact on delta in terms of the harshness of the sickness in breakthrough cases, but it might reduce the overall incidence and prevent the vaccinated from getting sick at all. However, the data always seems very weak, and always lags behind.
EDIT: definitely doesn't seem like getting vaccinated reduces the incidence, either: "three-fourths of the nearly 470 cases were in vaccinated people" from a leaked CDC memo: https://www.medpagetoday.com/infectiousdisease/covid19vaccin...