If Live Nation-Ticketmaster is not a monopoly then there is no such thing as a monopoly.
Live Nation-Ticketmaster only gets the monopoly power delegated from the artists and venues. If you break that up into competing ticket providers, that doesn't do anything to the underlying prices, tickets will still be resold on secondary markets until the prices reach supply-demand equilibrium.
Busting LN-TM hypothetically doesn't even do anything to the fees. The market is set by what customers will pay, and it doesn't matter to them what the breakdown is between going to the middlemen or going to the artist. At most, busting LN-TM does create competition for lower fees, so that the artist gets more of the revenue. But it's not clear at all that that's a matter for courts to forcibly impose.
(I see the downvotes. The Internet hivemind will always think it's entitled to ignore the laws of supply and demand, even on HN. Ticket prices are high because demand exceeds supply and customers choose to pay it, not because of a monopolistic reseller entity.)