Not really, because the game will end before any of the piles are empty if I'm losing, and I don't mind them being empty if I'm winning.
If you're losing, that depends on what the other player is doing.
It doesn't really, since I'm already playing the slowest strategy on the board. Either my opponent is playing something faster, or he's playing the same strategy as I am but he's just ahead.
It absolutely depends on what the other player is doing. As you buy expensive cards for Goons/Bishop, you are depleting those piles, making it easier for the other player to fully empty them
depending on what that player is doing. Yeah if they are going for Provinces then the game may end before any of the piles are empty. But they may be doing something else and empty piles may matter.
If you're winning then you are purposefully moving towards a game ending condition and proving the point.
Proving what point? That extremely slow strategies still want to end the game when they're ahead if they can? Yeah, that's the point I'm making. It supports the statement that extremely slow strategies are fine.
It proves that these cards encourage and enforce progression towards game end. However slow a game you can make out of Goons/Bishop, a cantrip +VP will easily and more often end up slower.
Right, I forgot that the trasher is still in your deck. Okay, basic Treasures aren't enough to guarantee making it work, but you really don't need a ton of support from the kingdom. You can end up in a stalemate with Bishop/Fortress because you can't have anything in that deck in addition to the combo pieces, but a cantrip +VP lets you have up to 4 dead cards in the deck without having to take even the smallest of risks, so it actually makes it easier to build a deck that does something useful.
With most trashers, you'll only have space for 3 cards (or else you risk drawing a hand of your trasher + 4 other stop cards). Even with 4 cards, I think you will regularly end up in situations where it's not enough to maintain a lead
and end the game. To end the game, you need to be buying stuff. To keep your +VP consistent, you'll need to trash the stuff you buy. 4 cards isn't much to be doing all that.
Also worth noting, this scenario pretty much assumes a close split, as it would just be too dangerous to let someone drive the pile uncontested and do nothing but generate 10VP every turn. Don't you consider that kind of centralizing monolithic strategy to be a problem?