>app cut fairly high

Same as Google's, so it seems standard.

>non-negotiable at 30%

Reduces for certain types of apps, given specific conditions, but yes for 99.99% it's non-negotiable. Still, it's their platform.

>arbitrary at best

I'd wager most rejections follow very clear rules. There are some head scratchers, but those aren't the norm, so "at best" is wrong.

>Who'd you think the EU would investigate for monopolistic practices?

Gotta have a monopoly in order to be investigated for it.