Anyone saying it's the dumbest thing Disney has done is over exaggerating- but so is anyone who says it fits Disneyland perfectly.
Yes, there are justifications that can be made to rationalize its addition to Disneyland, but it's certainly not a perfect fit and there are other lands that could have been much inside Disneyland.
As someone who is a big proponent (obviously), I will totally agree with you. Of course it's hard to change the knee-jerk reaction and therefore overall narrative, but we are well beyond that point so I do not mind opening up the vault of issues.
Star Wars Land fits Disneyland reasonably well. One of my long ago points was to people who were more than fine with Discovery Bay and thought SW:GE was completing ruining everything Disneyland stood for. That was a hypocritical viewpoint probably based on a preference for one IP over another.
Discovery Bay loses the genre narrative that defines Disneyland. While it did not have Jules Verne in the title, it really was a pseudo singular IP land. Perhaps some other non-Jules Verne property would have felt like a spiritual successor and it could therefore fit... but it was not totally a genre based land.
SW:GE flaw is that (other than being a single property), is sort of an amalgamation of three other genres. Fantasy, Wetern and Science Fiction. Those are already represented. Discovery Bay sort of did the same thing, more of a Historical/Fantasy/Sci-Fi blend. That's kind of why Jules Verne works well as a bridge between Fantasyland and Tomorrowland with 20K.
However, Disneyland has long since lost the original purpose of genre-based lands. Critter Country is not really a genre. Toon town (Animation) is NOT a genre despite what the academy thinks. Historical is a genre so I give soft passes to the Americana fuelled elements whether they be Main Street or New Orleans Square that actually kind of hosts a series of different 'genres' within its boundaries. By those declining metrics, I'm ok that Discovery Bay fits well enough and does not overall water down Disneyland more than other subsequent additions have. SW:GE falls into a similar bracket.
If we actually wanted a land that fits the purported original "Perfectly" it needs to be a hard genre that Disneyland does not currently have. Mythos or Horror being the two bigger ones that come to mind. For various reasons people no longer totally equate Disneyland as being appropriate for 'Horror'... that's simply because the natural land that fits perfectly was not with the original product. But there is a strong undercurrent of attractions that fall into this purview at other strong theme parks (Efteling has many horror attractions). Unfortunately, Disney is not Universal, but a very classic Monsters take would probably be the most palatable and logical addition. Transylvania being something that I think would aesthetically compliment what Disneyland currently has.
Things that are perfect are not always what people want though, they just want familiarity. That's why so many people wanted Discovery Bay. It was familiar, it was just more Fantasy/Sci-Fi. I'd argue that a perfect Discovery Bay locale would actually be the entire Motorboat/Autotopia/Subs plot.