Is 5e too hard? Eh. It depends. It can be very difficult, but in general it isn't. I will say, when playing Storm King's Thunder, we encountered a powerful blue dragon, and finding out that my Halfling needed to roll a 19 on the die (even with advantage) to save against it's fear aura was an eye opening experience. That a natural 20 doesn't automatically succeed on a saving throw means you can and will encounter a save you cannot make in due time (Paladins and high-level Monks notwithstanding).
There are ways to mitigate this, but again, it requires having optional features toggled on, or having the right guy with the right ability in your party. Which is the point I'm trying to make here.