When talking about costs, there are two separate concepts:
1) The cost to add the card to your deck
2) The cost to play the card
In MTG, cards all cost the same to add them to your deck, i.e. nothing. (meta-game financial costs notwithstanding)
In Dominion, cards usually cost the printed coin cost and a buy. Of course, gainers can change this calculation.
In MTG, the cost to play the card is highly variable.
In Dominion, actions can be considered to cost an Action to play, most other cards can be considered free once drawn. (All cards can be considered to cost "a card" to play.)
So trying to equate the "cost" of a card between the two games doesn't make much sense.
When people say that they'd rather have a Mining Village in their deck because it's "strictly better" than having a Village in their deck, it's actually the same as the MTG concept (since in MTG, cards start in your deck). Both cards cost the same to play (the card itself and 1 Action), with Mining Village having an additional effect.
But saying that this therefore means that Mining Village is "strictly better" than Village is incorrect, because the $3 price point of Village could be an advantage over the $4 price point of Mining Village.
So it depends on your frame of reference. When talking about cards in the Supply, you have to factor in the cost for the "strictly better" comparison. But when talking about cards in your deck, you do not.
When talking about the cards in general, they are not in your deck, so cost should be factored in. And by this view, there are no two cards in Dominion with one "strictly better" than another.
But when talking about cards in your deck, I don't think just saying "better" always captures what you want to convey. For example, Mountebank might be "better" than Fortune Teller, but it's not "strictly better", even when it's in your deck.
However, a Bazaar in your deck would be "strictly better" than a Village in your deck. If anyone has a term that conveys this difference more eloquently, when a card is like, pretty much always better (but maybe not in edgecases), but we're talking specifically about when it's in your deck and not just in the Supply or another pile, and without using the word "strictly"... please share it.