Ammunition being limited is part of the challenge. Try searching barrels and chests for more ammo and potions. Sneaking through the game is part of the point. Direct combat in later levels will get you killed in short order.
Thanks for covering it - but you missed the entire search mechanic. Stand next to a barrel and press F to search it for useful stuff like ammo and potions. That’s how you’ll manage to survive later levels. Ammunition is intentionally limited.
I understand your perspective, but the fee is so low (less than $4 USD) and will include all future updates and ports of the game to other platforms, including an upcoming native Linux version. I think the price is fair.