Discourse enforces to quote only a person at a time because you can click on the quote to get more context.
This is really the improvements on email quoting no repeat and reader choose the amount showed for the quote.
You can read from email if you activate it on your preferences.
Otherwise the accessibility has been taken in consideration by Discourse developers https://meta.discourse.org/t/accessibility-audit-and-shepherd-for-making-improvements/66620
Finally, I find that most of the critics say that Discourse requires a little bit more work to post a message. I think it is true, Discourse force you in the right way but it is for the benefit of the readers.