That's an interesting point-of-view. I was also worried and had to search in their Slack channel. This is what they have to say:

"so specifically to lock-in: right now, no one concerned about lock-in is going to have a good experience on dark. We don’t have the resources to address that need, but at some point we will be in a company position to deal with the lock-in question. Our plan is to give you tools and resources to move off Dark if you want to"