Artifact is too much of a weird anomaly to count IMO. It was more ambitious than your average hero-shooter clone, but they fucked up with one of the most pants-on-head retarded monetization schemes imaginable. I don't think audiences reacted negatively to the gameplay, which was fine if a bit too esoteric for its own good, but to the fact that the monetization model was outright hostile, especially by Valve's standards. By the time they released the rework, the damage was already done, and the fact that they refused to do anything with it afterwards didn't help matters. They could have easily turned things around with 2.0 (or Foundry), but they didn't even try.
Underlords was kind of the opposite situation, since it was more of a straight clone of a flavor-of-the-month thing that was lukewarmly received with a half-baked cosmetics-based monetization scheme (I'm not sure but I don't think you could ever spend a single dollar if you wanted to on Underlords at any point), but they forgot it existed at the point it needed support the most, and the patches when they still cared were almost schizophrenic in direction.
Both are examples of the problems with modern Valve's particular ADHD approach to game development, which is an entirely different beast from the problems of Concord-likes. Both failed more from a lack of interest from the developers rather than the audience, which is unusual to say the least. Neither was more than a side project at best for Valve, so I don't think the damage done was enough to consider them as much of a disaster as Concord or Suicide Squad or whatever. Both are still playable in some form if you hate yourself enough, so that also disqualifies them in my book.