Marketing is important, because if no-one has ever heard of your game they can't buy it. A lot of really good games have gone under the radar for that reason. However, you're right that marketing very often makes claims that are, shall we say, barely justifiable in relation to the facts.
There's no doubt a lot of people (Probably most of us) can be persuaded to buy things by good advertising, but I don't think it deters them from wanting other things, too.
You only have to see how things like Minecraft and The Witcher came out of nowhere to achieve great popularity because they were offering something genuinely new and people responded to that. The main initial 'advertising' for both was simply a lot of gamers telling each other how great they were.
I didn't think people are ever deterred from innovation. What they (We) all do, however, is continue to buy games that are often very similar to each other because we know we will like them.
There's interest in the new, but comfort in the familiar. That's just people
