Most people leave reviews to vent their anger, or express their joy, not for the benefit of prospective buyers. Whether we think that's good or bad is irrelevant; that's the way it is, and I don't think there's any way to change it.
People are smart enough to decide for themselves what the value of angry user reviews are. Maybe it's not valuable for a game's review score to be dragged down by backlash from a bad launch.... but then, maybe developers should invest more effort into not having a bad launch. This one was obviously done on the cheap; it's every platform that's having problems, not just Steam.
For the record, I'm not particularly angry... I had very low expectations for this content, since adding new leaders is just about the least impactful thing you can do in terms of gameplay, and when I saw the note that it would be free to owners of all the previous DLC, I had a pretty good idea that wouldn't go seamlessly. But do I feel sorry for Firaxis/2K? I don't see why I would.