Huh, cbexaminr why would you want to build GUIs without the sizers, they are such pain savers?
Because my brain finds sizers "too complex" to easily, quickly formulate form designs, and quickly experiment with layout changes.
There are, I believe, a lot of us left in the world who have successfully built forms without sizers for a long time.
I have played with them, but either they are a bit "complex" for Rapid layout changes, or my mind just hasn't figured out the correct approach to applying them to make this easy.
When I want a particular relationship between displayed items, I cannot simply grab (an) item(s) and move them to obtain that, I have to stop and think, ok, what combination of, possibly nested, sizing items are necessary to achieve that - and then in some cases, may still have to add additional spacers, which upon deciding to re-arrange may have to be deleted or altered (in addition to the primary components).
Sizers, in my attempts thus far, require more effort to use. _maybe_ they are better to obtain good cross-platform results, but if that is not a requirement or useful, then they appear to simply be more (mental) implementation overhead to use.
Oh, and some of us work for people who also find sizer-based form design difficult, and, are more likely to move to a different tool supporting a more familiar paradigm, than a different tool that does not.