I started working with Discourse and nodebb about the same time and I have seen a clear difference in how both platforms have matured, and as well as missing out.
Discourse went from Jeff's Forum Software to a real product for others. In making this change, they have built IMO far better setup, worked with cloud providers to have one-click options, forked and brought in-house popular plugins to be maintained, broke out of the 'how i want it' to 'you want it, we will build it'. Speed is acceptable. Styling feels limited. Mobile is positive.
NodeBB still has all the great things that caught my attention in 2014, but it STILL suffers from the same problems I had then. Out of date documentation. Documentation migration. Limited integration with cloud providers. High profile Plugins Abandoned. I love the speed. The mobile implementation is incredible. But I find myself having the same frustrations I had nearly FIVE YEARS ago.
While Discourse isn't perfect, they have built and matured as a platform, in both polish and reliability. When I get the 'New Version' for Discourse, I am never scared to click that button. I can't say the same about NodeBB. Nodebb still feels like most other open source software, exciting and interesting, but not reliable enough to make me jump in.
Another good comparison in maturity would be Ghost. I started using Ghost and NodeBB at the same time. Polish, feature additions and ease of deployment have all been things you can easily see that Ghost has improved over time. I don't see that same platform maturity with Nodebb.