To start with, the in-game currency is absurdly expensive: € 2,99 for 3(!) orbs, when you need 5 to summon 1 hero (with 3% chance rate for rare heroes and around 20-30 summons needed to summon one 5* hero), and after 3 years the company has remained deaf to the people’s complaints.
Now the Feh Pass subscription locks features freely available in other games (ability to chain maps automatically among them) behind a 10 euro/month paywall. This is is supposed to be a “better deal” (compared to the outrageous price of in-game currency), but is much too expensive for a mobile game in itself, 120 euro/year.
Stat improvements for older, but beloved heroes are also locked behind that paywall. In addition, subscribers get extra 2 slots to add “favourite” heroes, granting them additional stat boosts. (Non-subs are limited to one.) As if the power creep wasn’t disgusting enough already.
It’s a literal pay-to-win model now, invest your money into a game with developers that value their fans, and bother to listen to their concerns, complaints, and suggestions.