I think as a low-mid level player, blindly copying my opponent's strategy might sometimes be the best way to win the one particular game I'm playing in, but is not a good strategy for climbing ladder overall, because I will learn less and grow less as a player that way.
The only time I will do it is in a tournament setting, where the significance of the outcome of the match dwarfs the game's impact on my overall growth as a player.
Even then, at least half the time I have a better shot if I play the game on my own terms. Sometimes in tournaments against much better players I will see the other guy buy a card that doesn't make sense to me. If I could figure out a rationale for it, I think I'd copy, but if I can't, I shouldn't. I'm reminded of a chess tactic proverb I heard once that if a much better player offers you a material sacrifice, and you can't understand why, just take the material. Work with the heuristics that you have and that you have a dominating control over like "losing a rook is bad" and "Don't buy Counting House in a Mountebankless Province game".
In fact, in an extreme case, if I had an hour to teach my little cousin Jon Jon how to 1v1 best of seven Stef for a million dollar prize, I don't think any plagiarism of any of Stef's ideas would be involved at all. If I spent 5 minutes of that discussing what Stef might do, I'd point out that he needs trashing against cursers and not to choke onto Provinces and Duchies early if Stef is playing the long game, but I don't anticipate telling him to mimic Stef's play at all.