I hate to break this to you, but typescript ain't type-safe. There's a lot I like about typescript, but your runtime is still node, so any "type-safety" is mostly illusory. Not to mention every typescript codebase I've ever looked at includes a copious amount of Any, so...there's that.
Also, typescript has OOP support for a reason -- lots of typescript codebases make copious use of classes. Javascript tried to remain mostly functional for a long time, and people kept trying to make class-based OOP, so, they added it.
Finally, React is not a full-stack framework -- it's a framework for generating UIs. It has recently added support for server-side rendering, and NextJS has added support for that, but Rails and NextJS are very different. Rails is batteries included, NextJS is bring your own [everything] that happens on the server.
YMMV/to each their own/etc etc etc, but referring Rails as "fundamentally unserious" (github, stripe, shopify, i could go on) reflects the opinion of someone who either has an axe to grind with ruby/rails, or is willfully ignorant of it's capability.
Also, typescript has OOP support for a reason -- lots of typescript codebases make copious use of classes. Javascript tried to remain mostly functional for a long time, and people kept trying to make class-based OOP, so, they added it.
Finally, React is not a full-stack framework -- it's a framework for generating UIs. It has recently added support for server-side rendering, and NextJS has added support for that, but Rails and NextJS are very different. Rails is batteries included, NextJS is bring your own [everything] that happens on the server.
YMMV/to each their own/etc etc etc, but referring Rails as "fundamentally unserious" (github, stripe, shopify, i could go on) reflects the opinion of someone who either has an axe to grind with ruby/rails, or is willfully ignorant of it's capability.