So what is it exactly about 5E that is creating this slavish devotion?
I call it the World of Warcraft effect - though I'm sure others have a better, more business-like name for it, that's when I first noticed it.
Basically, MMOs before WoW were a bunch of small productions by small teams, and they all went in many different directions. Stuff like ShadowLands was different from Horizons was different from Meridian 59 was different than Ultima Online was different from Everquest was different from Star Wars Galaxies. Then WoW gets released - it has polished all the rough edges out (and all the individuality), creating a mass market leader with high production values that requires none of the genre knowledge needed to succeed. Your first days in WoW went really well and you felt powerful and capable. Your first days in Everquest or Star Wars Galaxies were terrifying.
Because WoW got mass market, other MMOs found that they couldn't appease the crowd of players that just wanted WoW, but different. The subscription service meant that players couldn't afford to try all of them and why would they pay $15 a month for some game that isn't WoW when they are already paying $15 a month for WoW? Some MMOs failed, others changed almost everything about themselves to be more WoW-like (EQ2 and SWG being the more extreme examples). Then, within a year, basically, the entire industry homogenized.
The same thing appears to have happened with D&D 5E. It is a slick, polished product that makes new players feel powerful and capable (except when they get wiped by the goblins in the first encounter of Mines of Phandelver, but then they quickly learn that the GM should fudge game results). All their friends are playing it. Critical Role is playing it. The bookstore carries it when it doesn't carry anything else. And it also has a semi-subscription model of new game releases every month or so. D&D is the first game these players encounter, and they expect everything else to be like D&D.
So, how do you fight the mass market normie appeal of something like D&D? Well, you can't. Even if you create a more polished product that is more mass market, you are still dealing with an entrenched audience who isn't exactly looking to try new RPGs. This is why I doubt there will be a D&D 6e any time soon - it runs the risk of alienating the group of new players who've never had to suffer an edition change before (I have to buy Ravenloft again!?). But something like Pathfinder 2e feels a lot like Everquest 2 to WoW.
You can do what some companies are doing, and making their games more like D&D. Symbaroum, for example, just had a kickstarter to make 5e rules for their game world. If you haven't committed to a system yet, starting with 5e with open up your potential market a bit more. In either case, you'll probably struggle to get the audience you want for the same reason that you can't make a better D&D. Symbaroum's attempt won't amount to much because now it has created confusion in the marketplace. You can't just buy something with "Symbaroum" written on it and expect it to be compatible with another.
The other approach is to do your own thing. You can develop a passionate core of niche fans. You'll never get mainstream success like D&D, but something like Blades in the Dark can support a company. Plus, with stuff like Kickstarter, you can build on niche fans to do your marketing for you, as people walk in and go "What does Powered by the Apocalypse mean?" Another advantage is that you don't have to support the entire ecosystem yourself. You don't need to have special dice, maps and miniatures, videos on how to play RPGs, GM screens - a bunch of generic ones already exist to support D&D (and D&D has its own ecosystem there which does benefit new players greatly, much like Games Workshop's paints/tools/tutorials/terrain support all miniature games ultimately).
Long story short, D&D is like World of Warcraft, or I guess something like Warhammer 40k. It is an industry unto itself, rather than part of the larger roleplaying games industry. Its existence both benefits other RPGs, while also limiting their success greatly. But regardless, it is impossible to compete directly with it, and I personally think making 5e rules for one's game systems is the height of folly. It can't be defeated except through its own sheer incompetence (which Wizards is trying their best at).
So what can you, yourself, do to get other people to play non-D&D RPGs? Basically, you extoll the virtues of other games every chance you get. Yeah, people will roll their eyes when you show up, but some of those details about the game will get through and eventually they be curious enough to either try it out, or familiar enough that it becomes something they recognize in other games. Basically, "Have you accepted Forbidden Lands to be your lord and savior? Here's a pamphlet."