I'm usually paranoid about vendor lock in, but I can't join you on this one.
Netlify assumes a version control repository that you can pull from, run a build step, and then host static files from. The build tools are open source, the output is static and trivial to download and rehost, and the repository is git meaning one clone is all you need to port to any other service.
It's not so much my code that is locked in, as that netlify has spoiled me by making deployment so streamlined that it would be hard to go back to manual deployment. This gives me another option, which I appreciate. That's all I meant.
Why do you worry about vendor lock-in with netlify? They host static sites, so you are free to go anywhere. Unless you happen to be using their other services which this doesn't address anyway.
This is my concern in a nutshell, unless someone has a tool that spits out a properly formatted .htaccess so I can migrate my HTTP headers and redirect rules.
Netlify's playground is easy to use for setting this up, but I'd also like to have this available in a standard format - just as an escape hatch in case I need it.