You still can, but you won’t be able to participate in the Pit or maybe NMD100 but even those aren’t the most difficult with a mid build. The trouble you’re going to run into is that you are required to run Pits to master work your gear and as they’re tuned currently there are only a few builds per class that are wildly successful there.
So, for all content outside of the competitive scene I think your can slap skills together and be successful but when you’re measuring yourself against others fun isn’t really the gage anymore but the highest level you can complete.