This is difficult to answer. OpenACS form builder is powerful (albeit dated) and delivers a lot. However, as with any framework, you are restricted to what it can do. If you need very unusual styling or element positioning, it may be possible that you have reached a limitation of form builder (I say form builder as I don't really enjoy using ad_form, as I find it less readable).
However, nowadays with heavy usage of JavaScript, it could be argued that there is less emphasis on a backend framework like form builder, and more possibilities to achieve your goals when combined with modern JS tools.
I must admit to being a little out of touch with the most popular web frameworks (node.js?) but I imagine their approaches are possibly quite different from how OpenACS works. That said it should be possible to create a "modern" website using everything in OpenACS.
(Vague answer to a broad question!)
Brian
