I'm definitely not a 5e apologist, and 5e isn't the system I'm running most frequently these days (looking at Call of Cthulhu, Dungeon World, and Savage Worlds). So my experience is that 5e, while being a juggernaut in many gaming circles, hasn't completely monopolized the hobby.
I would say that during the 3.x/d20 era, that system came closer to fully monopolizing the hobby. There were d20 variants of every genre (d20 anime, d20 supers, d20 Star Wars, d20 Call of Cthulhu, d20 Conan, d20 Modern, d20 Future, etc).
Today there are so many games. The rising tide of 5e, social media exposure, Kickstarter, and other outlets have increased the number of players so there is a wealth of other systems available.