You're missing the point. That's almost the same as the OS doing it natively and pasting into Slack. Except it adds one more step than before, along with permissions & pricing headaches. What's the advantage?
Instead of the native: Screenshot/recording --> clipboard --> Slack
Now you have Screenshot/recording --> clipboard --> Dropbox capture + permissions/billing --> Slack
Why would Dropbox insert itself into a process that works fine without it and adds no benefit?
It's like instead of copying & pasting a paragraph of text into Slack, you use an extension that makes a GDoc of it and then links to that. But why?