Certainly this will be a very relevant discussion topic in due course in the Dev forum, but this is also my current opinion as an ordinary user of XFCE 4.13++.
I'm sure the knowledgeable amongst us will know how to mix and match both gtk2 and gtk3 elements of XFCE in MX, but I'm just saying that from my own experience, XFCE 4.13++ as a whole (not mixed with gtk2 XFCE elements) is not all there yet, IMO. Of course, the XFCE 4.13++ I'm using is continuously rolling and being updated, so that could be part of the problem.