KC at Debt cost is an interesting idea. It would make the gaining less swingy but it would also make it easier to play (like with Pathfinding or Citadel, the trade-off between spiking early and building your engine is in my opinion quite interesting).
But D8 is too cheap, D9 or D10 are better.
I agree that snowballing cards like Artisan would not be appropriate at Debt cost. But Overlord is a card with Debt cost that is often purchased in the opening and a comparison with Band of Misfits reveals that, if the card were priced at an ordinary cost, it would cost $6 ($7 seems too much).
Royal Blacksmith is also fairly similar to Hunting Grounds so the comparison between D8 and $6 seems to be sound.
Note that I am not arguing that the different types of cost are equivalent, of course they are not. It is just a heuristic that can be useful when comparing cards of different cost categories.
Back to your card, precisely because it costs D8 yet is far better than a $6 it is too cheap. It is ultimately a risk management thing but TR variants can arguably be purchased after the first shuffle (with Shelters in the Kingdom you could even open Royal Academy) so you could argue that it is not that different from Artisan which, as you rightly said, would be crazy at D8.