No. It IS what is happening in tango. It's what is happening when I and others refer to being "off their axis", often what is called (as Steve pointed out) apilado. Both partners are leaning enough, from the ankle, that they are beyond the point of their own balance. They are leaning on, and propping up, each other. If one were to move away suddenly or disappear (not that it can, obviously, but for the purpose of explanation) the other would fall flat on their face...or have to take another step forward.
I know what apilado is but the apilado you describe is more like the
exaggerated form in show tango and poses. Milongueros dance apilado
but it isn't as extreme as you describe. It's variable too in the course
of the different movements. I dance apilado but I carry none of my
partner's weight.
I've given up on this now. Words in a forum fail to express a feeling.