great improvement on building an interface entirely with scripts.
its a tradeoff its easier to layout stuff but as you see you now dont have the backbone so you can not get dynamism done as easily, so in practice you kindof need to write script anyways to get the kind of organisatorial inner working that workg with script gets easier to do so now you spend 2 times the time developping.
Anyway you can make a mel script that lets you do the same resizing and moving around with mel as you do in qt designer, live have used one for ages. Thats not the problem (yes even existing maya elements). The only problem with maya is that its impossible to make new videget types, and querrying form elements is a bit limited.*
*tough this is a boon aswell as a bane because you can spend you entire life tweaking a gui widget and never gain that time back because good ui design is hard and only very few people can do it properly. See thing is a lot of people add a lot into their guis whereas the best gui has allmost no inputs whatsoever. Because you dont need them.
is there a way to do this from within maya after the UI has been loaded?
if you compile** and install pyqt then yes, otherwise no not much.
** well yes you need to compile it at the moment, and its a bit of a bummer. Making it impossible to send scripts to clients etc.