Another problem was that during the playtest, most classes only had one subclass. Except for the ranger and I think the cleric, there was only one displayed option for a class. So anytime a new idea was given, it was the only option shown.As a Dragon Sorcerer, it was more of a gish-type, and as you spent your spell points for the day, you'd slowly transform, taking on characteristics of your second soul. It was mostly a fluff thing, but the text spoke of poor sods who had fully lost control and been consumed by their second soul, leaving them as twisted monsters that could only be put down because the person they used to be had literally been eaten from the inside. That was a ton of really evocative, interesting flavor, and I strongly suspect that the vocal minority that spoke out against these things is why we got relatively flavor-light classes in 5e. It very much came across as people thinking that, because this specific type of Sorcerer was more gish-like (gaining armor, resistances, and melee attacks as it burned through SP), that ALL types of Sorcerer would ALWAYS be gishes, and that erroneous conflation plus the newness of the concept led to a massive overreaction. It seemed perfectly obvious to me that this was just one flavor of Sorcerer and that they would provide additional options.
And at least for my part...I was there and active on various places at the time. I saw the responses. A lot of people--many of them not even Sorcerer fans in the first place--took one look at this new and different thing and said, "No, that's weird and bad, just make the Sorcerer like what it was before." That sentiment, phrased a dozen different ways, was the common refrain, that both the Sorcerer and Warlock were too "weird" and needed to be made simpler and more straightforward. So WotC listened...and that gave us a Sorcerer that looks a lot like a weaker Wizard. And now we have these calls to delete the Sorcerer (or Warlock, or both) entirely, because it doesn't do enough to justify its independent existence. It's a vicious cycle; classes that justify their independent existence are "too narrow" or "don't fit" or whatever; classes that pass that bar are "too generic" and "should just be an X."
In other words, class reductionism pushes a Morton's Fork: "if the class is generic, it should be merged with other, similar classes to save space, 'cause we don't need redundant generalists; if the class is specific, it doesn't allow people to play it as they like, so it should be deleted to save room for classes with broad appeal."
Due to the fact that vocal community isn't that mechanically creative, this lead to a lot of "it's different. I don't want all the X to look like that. I don't like it."
If the playtest Sorcerer had a traditional Wild Mage along with the gishy Dragon Mage, the playtest sorcerer might have survive. I wrote speculative version of a healer/paladiny Celestial Sorcerer and a necrotic/vampiric Shadow Sorcerer on here or the WOTC forums and it was popular. But it was too late to prevent the "It's different. I don't like" survey responses.