Olivia, I’m sorry if I misunderstood your original question.
Are you having issues with the non-legacy import or is your question specifically that the legacy import “Eventbrite” tab is not appearing?
I glanced through the code and didn’t see anything that should cause it to not appear.
Please enable WP_DEBUG and WP_DEBUG_LOG and share any debug messages you see while visiting Events > Legacy Import, Events > Import, changing tickets quantity, navigating your site’s home page, events page, single-event pages, and any other of your site’s pages relevant to this ticket.