There is a valid argument that unlocking all heroes ruins the difficulty curve. Kingdom Rush Origins is designed to tax your resources. If you drop a fully leveled or Paragon onto the first few stages, the enemies simply cannot compete.
Who’s the best hero in Kingdom Rush Origins? : r/kingdomrush
: Some heroes offer abilities that complement tower defenses perfectly, providing additional damage, slowing down enemies, or healing towers. Unlocking all heroes allows players to find the perfect combination to improve their defense capabilities.