Apple makes big money from their ecosystem. Wireguard developer provides high-quality solution for free, helping to grow proprietary ecosystem, essentially helping Apple to make more money indirectly and directly (by giving 30% from donations).
In return developer gets tons of hate from users and from Apple itself in the form of delayed reviews, rejects and constant threat of violating some rule and getting dev account banned.
In my opinion, the only solution for this is to stop providing services for free and put a price tag on the app.
I understand, that developer is a kind, not-yet-burnt-out person who wants to be the world a better place by providing the free way to exchange information securely, but doing so for free for corporate ecosystem is clearly not sustainable, neither financially nor emotionally.