Perhaps based on the number of resources? Crystals or gems. Without spending them. True, this would be a different hero; perhaps only the name would remain.

Added 47 seconds ago

It could be implemented as "maximum X 2" after a series of victories, so it doesn't look like cheating.

Because the Dwarf only replenishes up to the maximum, the Elf could replenish beyond the maximum, but with conditions.

And although these are variations on a theme, it's hard to avoid them.

Yes. No unnecessary workarounds are needed. Even the existing features will be further simplified. It should be simple and clear for the player.

Added 21 minutes ago
Here's a draft:

Draylana was born on the northern coast of Irollan, which was rich in minerals. After another war with demons, everything was devastated, and the girl lost her parents. To restore production, the Elves asked for help from the most skilled masters of Ashan in this matter – the Dwarves. Along with the delegation, one woman also arrived; she took the poor child under her care and began to teach her the craft, which was difficult for a woman. To put it mildly, she was very bad at it. But when she took gems in her hands, they began to glow. Noticing this strange feature, the Dwarves turned to the rune priests to explain the reason. The Elf went to Greenhaven to the wisest masters and received a very useful skill from them – extracting mana from gems. The Dwarves did not want to let the talented student go, reminding her each time of the gratitude she owed, but Draylana was not deterred; she ran back to Irollan.