Yes, you are 100% right.
Those solutions would be perfect.
Here are the two issues, which are personal.
My youngest daughter wants to be picked up the entire time we sit next to her. (not an excuse for safety, but a good excuse if I can find another safe solution).
It is hard for adults to sit back there (They can't sit in the middle due to no headrest or shoulder belt, so we'd still have one impossible seat to get into.
We could put another carseat in the back row, and I could sit next to that...
But, I'd be stuck in the very back of the car when we have guests in town.
So, yes, this is ALL for my personal comfort. I don't want to sit in a 14 inch spot in the back row, and don't want to force any other grown up to do that.
However, when we don't have guests in town, (which only happens about once a month at the most),
I have 1-2 kids in the middle row, and one kid in the back. (with at least 1-2 spots open in the back row)
So, we're just talking rare times when as a family, we want to go out to dinner, or up to Santa Fe, or things like that.
It also works for my husband's truck. The booster is not recommended to go back there, and the vest will be far safer, now that my oldest has outgrown the Marathon.
And, it will work when we're trying to get 3 across when we fly to Grandma and Grandpa's without me stressing at the airport trying to get my seats to fit in the CRVs. (and rental cars).
I've been pregnant between two marathons with my hips sideways in the back of a rental car too many times. Not comfortable, or really doable. This is for those situations where I get the raw end of the safety and comfort deal.
This wasn't an issue before... i could do FF marathon, RF SS1, RF/FF Marathon. It was easy.
Loosing the SS1 and outgrowing the Marathon is what has caused all these "dramas" in my car-seat life!
Erika