well I normally work with the hyperlink shortcuts but our forum users just only dump the addresses they do have in their web browsers into their texts.
Modern software and browsers do often no longer URL encode a comma (the & is still URL encoded and the blanks replaced by underscores) since the browsers can work with the comma and the users would not know how to URL encode something manually.
So working with < > or to URL encode the comma is not really a solution there.
But since there are probably very rare cases with such a comma inside an URL I think there is no urgent need to fix this inside Discourse at the moment. I just wanted to bring it up to your attention that this kind of problem can occur in Discourse.
And thanks for your good work, Discourse is a great software.