I'll go one step further... Its function to separate a discussion from the original author can often be important.
In the case of hate speech, it's quite common for an antisemite to post something, for a Jew to reply, then get blocked.
Quote tweets allow someone to have a discussion separate from the author. That's the context I see it most in.
If there's another mechanism we can use for similar interactions, please, please show me!
Do we need to use screenshots?
Email style quotes would probably be better.