I think it's a double edged sword of Open-Source/FLOSS... some problems are hard and take a lot of effort. One example I consistently point to is core component libraries... React has MUI and Mantine, and I'm not familiar with any open-source alternatives that come close. As a developer, if there was one for Leptos/Yew/Dioxus, I'd have likely jumped ship to Rust+WASM. They're all fast enough with different advantges and disadvantages.

All said... I actually like TypeScript and React fine for teams of developers... I think NextCloud likely has coordination issues that go beyond the language or even libraries used.