Big 4 to BB ER

In short, yes it's fine, don't worry about it. This is not like pod shops where a new, unproven PM might get blown out in under a year. Also, the ranked thing might be a bit over played. If you're at a BB, you're going to be fine in terms of getting looks for exits and having a brand name on your resume. If this was a new analyst at one of the small boutiques, it'd be more of a risk. Plus, what are you comparing this offer against? If you have a ranked team recruiting you, that would be the safer way to go, but this is undoubtedly better than audit if you're trying to move into a public markets role.

Also, a new team is honestly kind of its own opportunity. The companies I know the most about are the ones I launched on. If you get to be a part of launching on your sector, you'll have a much better fundamental base. When you join an established franchise, it's more about learning how to assimilate to their workstreams as quickly as possible. The models and investment views are already established, and you won't have time to do all the reading on a sector/company that you have during a launch. Just my two cents.