I'm not so sure that many of the critics of DCA would've thought the initial offering at Disneyland was that great. Parks take time to grow up.
Well, sure.
But there wasn't really anything like Disneyland in 1955, and they quickly identified mistakes and worked to correct them, and arguably built a park that only got better for around 40 years. They had a budget that didn't *quite* allow them to do everything they wanted, but there was an emphasis on quality to the best of their ability. Even in 1955 with financial constraints, Walt was insisting on things and certain level of quality that others (i.e. C.V. Wood) thought were unnecessary because they weren't clear money makers or didn't really fit the budget.
Can't really say the same thing about California Adventure, where there were seven other Disney parks that already existed and were clearly superior, let alone other parks run by other companies. The Disney that conceived and built DCA had considerably more resources at their disposal than did the Disney of 1955. Rather than straightforward attempts to improve a flawed product, there was a lot of denial and saving face excuses for DCA before the original executives were canned and different executives admitted there was a problem. And there have been a lot of lateral moves or downgrades to DCA since it opened, certainly nothing resembling the outright improvement the changes to Disneyland represented for many years afterward.
And, of course, it's clear to see that TDS, which opened the same year, opened with both superior attractions, design, and detail. TDS tried to meet the raised expectations of a subsequent theme park, and many would argue it blew past those expectations. DCA...well...
So the "of course it sucked, Disneyland sucked when it opened too" argument doesn't really hold up to any scrutiny. It's not remotely the same playing field. And by the time it was 20 years old, Disneyland had already added the Mine Train, TSI, Columbia, Storybook, Alice, the Monorail, the Subs, the Matterhorn, the Tiki Room, Lincoln, the train dioramas, Carousel of Progress, upgraded the Jungle Cruise, added New Orleans Square, completely redone Tomorrowland, Pirates, Mansion, Bear Country and CBJ, and had been bringing back the improvements they could from WDW. DCA, in 20 years, prettified a few areas, added an ok nighttime show, added a few ok dark rides, and built Cars Land, then set about ruining a lot of the improvements they had just spent billions on a few years ago, while problematic areas like Hollywoodland have still hardly been touched.
DCA has always existed in the context of a much richer company than the one that built so much of what made Disneyland great. So what's DCA's excuse for such enduring mediocrity?