What a pointless claim. Developers get charged, not the end user. You pay the same price as elsewhere, in fact Steam requires developers to price the same if am not mistaken. Besides what's the charge? People are willing to pay more for product they enjoy? If that's the precedent then Apple will go bankrupt day after this lawsuit is won.
How is it anti-competitive. No one is forcing developers to publish on Steam. It would be one thing to have a monopoly like Apple does and no other way to install. But they don't. Developers definitely have a choice whether to publish on Steam or not. Cost of publishing might be high, but that's no different than self-publishing and spending money on advertising. It's just operational cost.