That only works to a certain point. The demand is always going to be strongest for the newest attraction, and usually exceed the capacity of that one singular attraction. Adding more capacity certainly helps in some respects, but when everyone in your park wants to ride TRON and Space Mountain becomes the second tier disappointment, you gain very little in moving people around.
And worst case scenario, now that people are jumping hurdles and spending all their time trying to ride TRON and Space Mountain and Mine Train, you end up with things like Carousel of Progress and Small World that no one cares to see anymore.
Dude, when was the last time you saw a wait that was more than the time it took for the next theater to open in COP?
What were the fashion trends that decade?*
There are still going to be plenty of people waiting in line for all of the mountains after TRON opens - don't you worry.
Peter Pan's Flight will still have an hour+ wait.
Maybe It's a Small World would go back to having a queue that fits inside the building (like it did for decades before FP+ pushed it out into the already now-too-crowded walkway (pre-COVID caps, of course) if they added something
new (an addition - not a replacement) to the park every three to four years.
I don't know how that's a bad thing.
As for demand being the strongest for new attractions, that's true but if the "new" attractions weren't the same for the people who all visited that last time a year ago, five years ago, ten years ago like they are these days (because Disney slowed expansion down to a crawl while turing most "new" things into replacements rather than additions) that would still be spread out way more.
Go count the number of attractions
per-park at Disneyland and then come back and try to continue this argument with a straight face.
*Don't get me wrong. I love COP but it's a high capacity attraction already waiting for guests most of the time - possibly one of the only ones in the park like that, today.