I think to answer this properly you need a different, better-informed kind of fan than me. Probably the answer would involve digging through a bunch of contemporary magazines.
I've never heard, though, that it was poorly received at the time. When ZZ aired, there were older Gundam fans, but nothing like the kind of demographic spread that a forty-year-old property can muster. The first animated stirrings of an impulse to serve up Gundam for an older audience, and to focus UC material on the One Year War, are close in 1986, but they haven't arrived (0080 started coming out in 1989, though you could argue CCA ticks the first box).
And exactly what (TV) Gundam was meant to be was in some ways less defined. I've thought about this before in connection with, of all things, the design of the Zeta itself: it's kind of a non-traditional Gundam design in various ways, right down to the bird-skull head, but of course many of the things we use to understand 'traditional Gundam design' postdate Zeta and ZZ.
I'd gladly defer to anyone who knows more about this than me, though.