I have no sympathy for their concerns. I can download apps on my MacBook machines all day from many different sources, and it harms no one. While I understand the associated risks, computers have been this way long enough that the free and fair use of software on my devices is far more valuable than the brittle safety a marketplace offers.
Apple's greed knows no bounds, and while I'm no big fan of the EU, there are some regulations like these that ensure these big bears in the industry can't abuse their positions for profit, at such unreasonable expense to consumers (not always monetarily, but be it fair access, availability, and choice), and developers especially.
If commercial real estate charged XX% cuts of all sales from a business, every business would crumble with enough time, and only the big hitters would succeed with great resentment towards their gracious corporate overlords.