In all honesty, just being able to work with % when sizing things (forget about em, rem, etc) would make a WORLD of difference.
Add to that floating and positioning (not just absolute positioning to the browser) and aligning not just text but widgets and dynamic panels.
When it comes to displaying a site/web app, breakpoints are not enough.
I have used 100% width for some things, which helps simulate a little fluid behavior, but in general, when you are talking about all the components in a page, that is not enough.
Pinning to a position in the browser also adds a lot of issues, especially when you have to scroll.
I sometimes reach a point where I seriously consider just tossing Axure and just putting together HTML + CSS + images to produce a prototype for a project.
I just needed to ask. Why is there not an option for at least % as a unit for sizing things?
For instance, I have tried by using Window.width*x.x to simulate a bit of a Fluid behavior, but it doesn’t help if I have associated widgets or elements that need to FLOAT or ALIGN with that size change.
Also, when you are putting that on a Window Resize and you have Breakpoints, then you have to work with separate versions of the widget, not instances, so the page doesn’t break or the sizing is completely off depending on the Breakpoint.
Is there a way I could do that with variables? Float or Align I mean, depending on the browser window size?
Very frustrated. I get the benefits over something like Figma. But there are also a lot of downsides to Axure 
Some basic CSS would be a game-changer!