This is about more than fees, and the remedies need to be as well
Even before the merger, AEG livenation and Ticketmaster had the market stitched up. After the storm of the last Ticketmaster trial blew over, they were careful to carve out a symbolic selection of venues they didn't control. That's not a meaningful gauge here, it's just a straw man.
Ticketmaster's role has continued to shift over the years, and in the current version they are the punchable face to what most people hate about the modern music industry. Don't fall for it. Yeah they are eminently hateable, the fees are bullshit, their website uses every dark pattern and fraudulent trick in the book.
But that is a small part of the problem. The other two legs of the cartel own a ton of big venues, and have others locked into us or them contracts. Sports, concerts, venues, large festivals and most of the acts from whole music companies all tied together. Each paying kickbacks to Ticketmaster, the labels, the venues and in many cases the bands. Money shifts around to evade oversight, and help the record industries notorious accounting practices to siphon all the revenue past operating costs into tax havens and shady accounting.
At the core of it, driving the core of all of this and driving both costs and desperation is the fact that huge amounts of tickets have been presold or preallocated. Some go to the venue, some to the promoter, the band, the label, and a constellation of other players. This causes the show to instantly sell out, when Ticketmaster steps in and double dips by taking a cut when these players trickle their pre-allocated tickets into the marketplace at a healthy premium.
If you want a nuts and bolts breakdown of exactly how the cartel operates, take a look at the excellent reporting on the flows of tickets for the recent Justin Bieber tour instead of Swift. She is venting because Ticketmaster screwed up her presale and pissed off her exceedingly rabid fans, which she didn't appreciate. Bieber was in on the whole thing, and as big a willing participant as anyone else. (He also used to spit on his own fans, so is it a surprise?).
Any company or cartel of companies that controls both the vertical market and most of the horizontal market needs to be broken up. AEG and Live Nation ows venues, tours, sports teams, events and management. By tying control of those assets to ticketing, they control the allocation, sale, and resale. Any attempt to blame resellers is a farce. They extract a cut from resold tickets, and were caught telling the resellers they themselves blamed to create multiple accounts to get around changes that Ticketmaster was making to ensure the resale status quo was maintained. Acts that make waves or don't want to play get shut out of a huge swath of venues, as well as participating in group shows and festivals.