How really is FX better....

There are plenty of positives about DX bodies and lenses. If those positives appeal to you (i.e., smaller size, increased reach with telephoto lenses just to name two), then I can't really tell you that FX would be a better fit for you.

For some people, the even smaller portability of mirrorless is worth the tradeoff. It all depends on what best fits your everyday shooting needs.