In practice, the fees in traditional e-commerce systems tend to be significantly higher than 2.5% (I say this as an artist running a Shopify print shop for a few years). Some services like Bandcamp are upwards of 12-18%.

Hicetnunc fees are fixed, and the free market gives an opportunity for other platforms to improve on this if the community desires a marketplace with lower fees (it's much easier to build an alternative to Hicetnunc than an alternative Stripe/Shopify/PayPal). Artists are also given a 10-25% royalty (which they decide) for each resale of a token on the Hicetnunc marketplace. And, of course, since it is all peer-to-peer, you are free to exchange art tokens with no fees at all, save the negligible protocol/transaction fees.