IS .. is NOT
It is NOT that black and white When installing on older machines my first choice is Xubuntu. My rule of thumb is dual core and a gig of ram for Xubuntu, can be done with less, but this is my choice. Single core and less than a gig of ram = Lubuntu.
My machines are all dual core or dual processors, oldest machine being a 2005. All run Ubuntu (Gnome) and does not fit your 'is, is not' equation.
To buggy .. less buggy
There are thousands of happy Lu and X users out there or they would of never made the cut. So I would say that is personal opinion, not fact.