Being promoted to O-6 isn't that big a deal.
Over the 7 years that I was in the Army I knew at least a dozen full colonels who were parked in meaningless jobs. They were, for some reason, never going to get promoted to flag rank, but they were being allowed to do their 30 years and collect their 75% retirement pay. When I was stationed at Ft. Riley, KS, I knew a full colonel who had a make work job that allowed him to fish and hunt during most of his duty hours. He only wore his uniform into the office one or twice a week, otherwise he wore civilian clothing and did whatever he wanted to do. I always thought that it was a waste of money to park those senior guys in meaningless jobs. Most of them wanted meaningful jobs, but they knew that they weren't going to be promoted or given meaningful assignments, so they were putting in the dead time in order to get to 30 years and the 75% pension.
It’s not just officers, it’s common with NCO’s as well. IF you’re a good guy.
I spent the last six months of my deployment on easy street, making bird houses, drinking coffee, working out and basically just living it up with a couple of other good NCO’s in similar situation because we didn’t have enough time left in to go anywhere meaningful.
OTOH, If you’re a schidtbag, they’ll find the nastiest, most god forsaken duty that no one else in the battalion wants and you’ll be stuck there till the end of your deployment. There were several like that as well.