1. JS has a lot of quirks, but you can find quirks in anything that has been around for a long time. From just using a linter you can avoid a TON of problems (and realistically, how many people code in any language without any kind of linting?).

2. I don't know what to say about this. Maybe historically, yeah. But nowadays? You can build your API with any language or framework, and have nodejs running an isomorphic app. This means you can do server-side rendering and then delegate to the client once it loads. This provides the best possible experience. And you avoid code duplication, since you can run the almost the exact same code on the server and client. (You'll usually have to do some minor tweaks, which I'd consider reasonable.)

3. From what I've seen, complex UI interaction are difficult to do well regardless of your environment. (This is also why I've been really excited about react+flux, since it provides a much better experience when developing applications.)