It's decent in a way; I'd rather have the band, venue, and Ticketmaster make money directly than scalpers indirectly, but I can't really complain that people pay the prices asked; if they didn't eventually the prices would start dropping.
In an ideal world, TM wouldn't have a monopoly on ticketing for large venues, and artists wouldn't be forced to work with them. Artists and venues could still charge whatever "dynamic" price the market will bear, but competition in the ticket space would hopefully push down the cut that the ticket distributor takes. I'd imagine this is why artists are generally unhappy with TM's monopoly, since they don't have much leverage here once they're booking venues of a certain size.
But TM's monopoly is here regardless of how they price their tickets. And in a world with that monopoly, TM's dynamic pricing model benefits artists more than the previous model, even if it isn't the best possible arrangement for them.
I guess the main argument is that anything a monopoly does to increase its profits is bad. That's fair -- TM makes more money from this, and they'll probably turn around and use that money to strengthen their position (e.g. sign contracts with more venues), making it harder for any competition to challenge their monopoly. But that's a really broad issue. Dynamic pricing itself seems...fine