Is backend development really more difficult than frontend development?

It really depends what you mean by difficult. They’re both difficult, in very different ways.😀 

Backend development is hard in the way that, say, advanced calculus is hard. It’s a complex discipline that requires a lot of time and brainpower to master.

Frontend development is hard in the way that, say, dealing with the IRS is hard. It’s, you know, mostly red-tape and working your way through a system that seems inherently out to get you.

Both take a lot of time to master, for very different reasons.

These are generalizations for the typical use-cases, of course. You can do wonderfully complicated things on the front-end, like writing WebGL applications, but that is certainly the exception, not the norm.