GM might be sometimes better than Lab but on average it is clearly worse so the claim that Grand Market is "super better" than Lab is about as truthful as the world is flat.
Sure, that's why Lab costs more than Lab and has a no-Copper buy restriction. Oh no wait, it is the other way around.
Man, that Donald X. must be pretty bad at that game designing thing if he prices his cards so badly. Or some random guy on the internet is wrong. I wonder what's more likely.
Yeah and Chapel probably sucks too because it only costs $2, right?
Chapel is an exception. In virtually all other cases price and power are highly correlated. There is definitely no card in Dominion which costs 5 and is "super better" than a card which is priced at 6 (and would be priced at 7 or 8 without the copper clause). There are of course situations in which a Lab is better than Expand or Prince but Lab is in general worse than either of those cards.
That Grand Market is generally better than Lab is an obvious fact. At least this preposterous discussions shows that mirror universes in which fair is foul and foul is fair do exist and that communication between our world and topsy-turvy land is possible.
Cost not correlating with power isn't just "well chapel is an exception". Cost controls a few things: 1. perception of power 2. accessibility.
The classic example isn't Chapel, but Courtyard. Courtyard is a stronger BM card than Smithy, by quite a lot, but costs $2. Why? It's simple - BM strategies don't have extra buys (usually). So any Action you're buying costs "all the money in your hand", so Courtyard costing $2 doesn't make it significantly more accessible. But in engines with many gains, Courtyard isn't significantly better than even Moat, so being able to buy multiple Courtyard for cheap isn't a big deal.
We can also consider 3 cost cards, where the top 5 3 costs are certainly better than the vast majority of 4's, and the primary difference in costing 3 is that these cards can be opened with twice.
Anyhow, you have an interesting definition of "obvious" and "fact" here. It's kind of douchey to conflate your own opinion with objective truth, tristan. I think Lab is ultimately "better" in the sense that is more often a more important card. Why? Because while GM provides a lot of valuable resources, the only *scarce* resource it provides is +Buy. You can get coins from any number of sources, and while GM is a strong source of coin, it is somewhat frequently not fast enough to justify going out of your way for it. Lab is one of, what, maybe five nonterminal draw cards in the game? This is huge! Even terminal draw is a scarce resource, and Lab is one of the very, very few cards that gives you a solid chance of building an engine without any real +Action. That's amazing.
Regardless, all of this is much different than the original question, which is whether or not Festival is as good of a Village as Village. It's not. It's because it costs too much and it doesn't draw. That extra card is really important - finding another Village or Smithy in a 4 card search area is much easier than a 3 card search area! If your payload would otherwise be Silver, and you don't have other 5s to buy, then of course get Festival, duh, but it's really a Worker's Village that always draws Silver - not ideal for a lot of decks, while pretty decent in some.