The beta players said that Valve largely ignored their feedback, and only made trivial changes. Richard Garfield said in an interview that people consistently didn't like some aspects of Artifact, but that him and his team knew what was best for the game, so they mostly disregarded complaints about RNG and some cards being frustrating to play against.
There were unrealistic expectations about Artifact. Some of the people in the beta couldn't stop singing its praises, calling it the best game ever made. After launch, one of the other beta testers said that a lot of the people publicly praising the game had privately said that they were trying to use the hype around a new Valve game to launch a twitch/youtube career, and they didn't actually like the game. There were also features present in the beta that had been silently cut before release, and some game breaking bugs that were present in the beta, and never got fixed.