We used to go to WDW the last week of August every year (skipped 2020, unfortunately). Yes, it's really hot, but I wouldn't say it's hotter than July. We went mid-July in 2019 and it was just as hot then as I remember any August. Our strategy was always to get out early in the AM, take a long afternoon break and then go back out around the time the sun was going down. It usually rains every afternoon as well and it's hurricane season. The heat definitely impacted how much time we spent in the parks, but the crowds (at least during the last week of August) were always quite low. We also enjoyed being able to go to
MNSSHP when they started holding it in late August (not sure what's happening this year). Is it the best time to go, weather-wise? No. But if you can strategize around the heat and rain, you are typically rewarded with lower crowds.