This is not true. I will not touch anything in Orlando from late April to late October. Period. Not even if it was free park tickets and they paid me large sums of money by the hour to sit in the parks so yes, heat will stop visitors.
Sure, overall, we know less people are going post pandemic, but of the subset of people that still go, many are moving out of the summer months because we just don't want to deal with it. That leads to softer attendance in the hotter part of the year. Of the people who will still subject themselves to Orlando in the summer, many will skip a day or cut a day very short if it is hot further decreasing attendance. Finally, the locals will not show up in high numbers on the brutal days which also drives attendance down.
Heat absolutely impacts attendance and it is a problem all of the Orlando area parks are going to need to address at some point.
Roberts over at Comcast even said heat was driving down their attendance last summer so this isn't unique to Disney. Sure, both CEOs may want to play it as if that is the ONLY reason, which we all know it isn't, but it is certainly a reason that has a large enough impact to discuss.