There was no goal of buffing or nerfing any cards; that was simply not a factor. In all cases the goal was fixing problems.
- Hermit being heavily nerfed, as you can no longer exchange it for a Madman if you buy an Event that gains cards, or play a gainer like Horn of Plenty in your Buy phase. Nor can it use the Scheme or Prince trick to both top-deck it and gain a Madman. The only upside is that a Hermit who goes mad returns to the supply instead of being trashed, making it possible to have more of both cards.
What you call "heavily nerfed" I would call "identical in most games." Most games do not have an Event that gains cards to use with Hermit.
Whereas, every game with Hermit has the Hermit pile, so Hermit now returning to the pile and so not limiting you to 10 Madman plays per game is a significant change.
But again, the point wasn't to nerf Hermit (a super-strong card); the point was to have a better wording for it.
- This also nerfs Exploration significantly for similar reasons.
Again most games Exploration is not paired with an Event that gains cards.
- Bonfire being nerfed. This isn't such a big deal as I normally just use it to trash Copper anyway and it's still a good card but the rule change seems unnecessarily.
Trashing arbitrary cards from play breaks the game. That's why I changed it; to not break the game. Going into play uses up a card for the turn; taking it out of play lets you reuse it and generate loops.
In this particular case I could fix this while having almost no effect on the card's gameplay; you were already trashing Coppers with it.
- Normally errata in Dominion simplifies cards but this seems to have done the opposite with the presence of "non-Duration actions", which seems unnecessary to really refer to, along with "gain a card you bought", as I cannot see any problem with the original wording, which was the much simpler "buy" and means the same thing.
"When you buy this" and "When you gain this, if you bought it" are in fact not the same functionally. They happen at different times.
And that's why those cards changed; because so many players conflate buy and gain, and are confused when Workshop on Ports doesn't gain them one, or when a when-buy trigger happens before a when-gain instead of letting them order it, and so on. In a few cases I could not just use "gain" as it generated loops or other problems, and so those have that awful wording, "when you gain a card you bought." A few of those are "When you gain a card in your Buy phase" instead, which is simpler but was again not always usable.
