They should think about what happens when expectations are so high that a single dev must deliver and maintain multiple products. What stops that single dev from leaving and offering the same product on his own.
I think the part you can't easily clone will turn out to be the institutional processes that allow you to run at scale, onboard new people, deal with common requests that AI cannot on its own (e.g. legal compliance), the relationships you have with partners and vendors, the legal setups you have in place etc.
I'd assume that plenty of developers feel capable to building a better jira, and some try, and few/none succeed despite atlassian doing everything in their power to drive clients away, because cloning the project isn't the hard part with that type of product.