You’re definitely warm. I worked at Dropbox around this time and there was very little C++ or systems experience in the building. I think it’s expertise they tried to build but for whatever reason didn’t. I work at Facebook now and the difference is night and day. FB does share a ton of code across platforms, and it doesn’t even feel controversial.

I don’t think Dropbox made a mistake in cutting out their shared C++ code, but I would caution against generalizing code sharing as a bad idea.