I need a solid argument to explain to people that aren't necessarily tech-savvy as to why we should choose Rails over Nodejs
Hi Max, it sounds like that you are proficient in both stacks and probably have a higher expertise in Rails (correct me if I am wrong) and since you are the only dev on a project, a good argument that comes to mind is probably the velocity and maturity (enterprise grade, battle tested in production) that Rails provide with proven success stories in the tech industry such as Airbnb, Stripes, Shopify to name a few.
You can also make the argument that Rails is great to run the backend and React+Vue (and nodejs for tooling) is ideal for the front-end development (see or find companies example that use both). You can also build and show a prototype using both and share your experience which could help you find and forge the selling points to those non tech savvy folks, why not.
Eventually, are you going to have other developers on your project? if yes then you will need to take in account, onboarding and ramp up to contribution time when they are hired.
IMHO, I am not a fan of the debate Rails vs Nodejs, they are just tools at the disposal of the developer it's just a matter of figuring out what makes the most sense.
Let me know if you wanna discuss further, happy to help out!
ps: markdown preview on stack share... no good.