The existence of restaurants doesn't imply that people don't cook their own food. That people have long come up with their own solutions for the problem that Dropbox addresses isn't incompatible with the notion that Dropbox can be a successful product. Obviously.
The world is packed full of products and services that do things that people can easily do themselves, because plenty of people are happy to not have to do that thing regardless. That's Dropbox's target market.
This is the part where he loses any sympathy.
If it’s so trivial why was nobody doing it? It’s classic tech bro know-it-all-ism.
Plus yeah wow, without the 3% of people who run desktop Linux whatever will a business do?