They can, and are, both weasels. Apple wants far too big a cut for what is essentially a tool chain that other charge at most 1500$ for, and some code review to screen for some basic and dire crap. The rest is basically extortion and rent seeking. Forts counter claim is laughable, as nothing they do requires unsupervised installation rights, and they shouldn't ever be trusted with them. I shudder to think of the wallet draining, ad slinging, and privacy raiding mess they would make of things if left to their own devices.
That said it's probably a (weak) negotiating strategy to lobby for a settlement on more reasonable middle ground. But the are NEVER going to get what they are currently asking for.
But what Apple wants to take out of the subscription revenue vastly exceeds what they offer in services for an app store with broken search capabilities, and vendor lock-in for payment processing. What you get for that 30/15/10$ is to be allowed, begging tin in hand, to access their base of millions of customers stuck in a walled garden they control. (and to be fair, the dev tools, but as I said their not worth paying points for)
Apples constant attempts to compare themselves to a book publisher are ridiculous, as a publisher had to pay to print an actual book, distribute it, promote and advertise it, handle the accounting, and in many cases, paid advances to the authors to allow them to complete their projects.
A game distributor that is paying out cash at every development milestone may be entitled to 30% or more off the top. The chance to be included in an algorithmically selected "top apps" list doesn't even justify a percentage point.
As far as this fight goes, I'm not rooting for either side at this point.