the developers still need to work on big patches, content and fixes even years after release

Why would they need to do that? If it's years down the line, there shouldn't be any bugs left to fix by that point. And offline single-player games don't need regular content drops. Sure, an expansion or two might be nice, but those don't come free. Only online games need to constantly feed their players new content in order to keep them hooked and coming back to buy more MTX.

Would the average consumer willing to spend more for a game with everything in it? AAA already cost 70$ at launch, would the average consumer accept further price increases, or would selling plummet in comparison with reduced price+dlc or free to play with microtransanction?

Oh sales would plummet for sure, but it would still make a profit, just not as much. If From Soft and Larian can do it, everyone can. They just don't wanna. (see below)

At the end companies are not inherently “evil” they just look for what works and what doesn’t by trial and error

That really depends on your definition of "works". Sure, it's a business, but what's the goal? To me there seems to be a noticeable difference between companies that want to make good games, for which the business side of things is just a means to an end, and companies that want to make as much money as possible, where the games are the means to that end. Is that latter category 'evil'? Maybe not strictly speaking, but I have no concern for those companies whatsoever, they can go fuck themselves.