You might want to check out the Qvist rankings. I'm not sure the 2016 rankings are complete, but the 2015 rankings are here:
http://forum.dominionstrategy.com/index.php?topic=14011.0Since they're grouped by cost, that makes it a little more difficult, but at least you can get a feel for how the community rates the cards. For example, you'll see Cultist above Torturer on the $5s. It's non-terminal for other cultists, doesn't give the junk to hand where it can be paired with a trasher, and doesn't have an escape clause. No contest. Even though Torturer is a draw-3, if there's a village on the board, you're sometimes better off playing village/cultist-chain/village/cultist-chain. Think of each chain as though it was a single terminal draw "package."
It's harder to compare $2 and $4 cards like Chapel and Remake directly, but I'm pretty sure that everyone would agree that Chapel is by far the more powerful card. If you see them together, you skip Remake the majority of the time. I know what you're thinking. Estates become Silvers. Eww. Forget that. Take the Chapel chainsaw to your deck and lose the starters.
Remodel is emphatically NOT a trasher. Expand is not a trasher. These aren't even considered middling trashers.
The purpose of a trasher is to thin your deck, and upgraders do neither. Any card that upgrades "up to" an amount more requires you to gain a card, meaning your deck will never get thin. Some upgraders that say "exactly" an amount more, however, can be extremely useful. Upgrade itself can get rid of all of your coppers if there is no Poor House in the kingdom and will thin your deck nicely.
The title of your thread is "comparing power cards" but then you list a kingdom with several decidedly non-power cards on it. Warehouse, Remodel, Salvager, Lost City, Altar and Expand are definitely not power cards. They're all good sometimes and they all have their place, but they're not cards that make alarm bells go off when you see them.
So definitely do some reading.
As far as comparing power trashers goes, I'd rate the trashers in this order:
Donate
Chapel
Steward
Remake
It gets a little muddled after that.
Temple?
Plan?
Bonfire?
Junk Dealer?
Count?
Trading Post?
Forge?
I'll give Mercenary props, but you can't just buy one, so it's a whole different thing. Ambassador is also one of the most powerful cards in the game, but it's hard to get thin with it because you can pretty much guarantee that your opponent is handing you junk as fast as you're handing it back.
The key is the ability to trash multiple cards with each use, ideally gaining nothing. You can get thin with trash-ones like Trade Route and Salvager, but you usually have to buy two; if you're doing trash one/buy one each shuffle, it's hard to get thin.