The thing I remember about really old versions of Gnome was that it expected the local hostname to resolve before it could get anything done... which for all I know, might even work 'seamlessly' on a Linux system with whatever resolver library's linked there, but on BSD, it induced about a 50-second wait at startup before anything could be done at all. (Obviously installing tinydns would've been a quick fix, but at the time, I didn't know what the hell I was doing yet.)
Bluntly, both are Really Big Environments, and just like MacOS or Windows, they suffer the same problems. The upshot is that things like twm, AmiWM or even XFCE are available and 'supported' just as well as the big offerings. (Well, if you want dock or tray apps, you need to pick something subscribing to one of the major dock or tray standard(s) around.)