Same with buying 3 ironworks with something like great hall on the board. You ironworks yours, I can't afford to let you have them all, and you just changed the game to piles and estates.
Why can't you afford to let someone have them all? Look, it takes you three provinces to have the same number of points as all eight great halls and all eight estates. It's a strategic decision - you can either join the other person or go for a different strategy.
If IW/great hall really is the right strategy, and you both think so, then yeah, you should both go for it. But if you think it's a bad board for it, then don't mirror them! Just beat them normally, with provinces!
BTW, I think just plain big money - no other actions even - beat an IW/great hall/estate rush, on average. You should be able to get a few provinces and a duchy or two by the time those piles are empty, because all those score so low, only a few provinces is enough. If you throw in a single good card - a smithy, say - it turns into a blowout. IW/GH rush is pretty weak. It's a few extra points, but not many, and you spend like ten turns to get these one-point cards. And if they're not emptying those piles all the way, even better, because you have a huge lead in getting to like six provinces.
I'm not saying there aren't times when piles and estates aren't the way to go, like with seahag or gardens in the cards but taking a nice board and changing it to a stupid race for the low cards says something about the style of player.
What does it say about them? I don't actually know what you're implying there.
The times where piles and estates are the way to go is when that is faster and scores more points than going for a long game with provinces...
As a rule of thumb, think if you would do it if you were playing in real life with a friend.
Yes, we'd do all these things IRL with a friend. Or, I would.
It's part of the game, and the variety of Dominion is what makes the game so great! Some games are curse-heavy no-trashing sea hag slogs, some are mega-turn Grand Market-KC games, some are rushes, some are engine games, and some end up simple big money plus one card or two. And some games are unclear - multiple paths seem viable, and you're never really sure whether your path is better until you play it out and see.