Can you explain how Zulip is more like a better IRC and Mattermost like Slack? I'm a reluctant and weak (opposite of power) user of IRC and Slack and though I

Can you explain how Zulip is more like a better IRC and Mattermost like Slack? I'm a reluctant and weak (opposite of power) user of IRC and Slack and though I understand their great architectural differences, as a user they feel very similar. Surely I'm missing something.