There are two ways that you could accomplish this quickly and easily
- When you bring someone onto your list, presumably they are being tagged with something, correct? That Welcome email could be included in your delivery sequence and then use the filter on the first email to exclude anyone with that tag.
- If you have a visual automation driving this delivery of these quiz results, then have a condition to check for the existence of that tag and if "no" then send a separate Welcome sequence email. Then under that conditional check where everyone falls through no matter which side they go on, you send them the quiz result sequence.