If you buy a Leeching Felhound, you take damage but it doesn’t proc Keyboard igniter.
The text says “If you take damage since your last turn”, so it should.
“paying health” is not the same thing as “taking damage”.
Yes , paying health is the same as taking damage.
No, it is not. The game designers said so, and they make the rules.
Both of those things cause a REDUCTION IN HEALTH. But there are lots of ways to reduce your health, and not all of them involve taking damage.
The developers said that this is not the same thing. Try to make your own game with your own rules if you are unhappy