We always went to Florida in the June-July-August time frame.
You are right it is very very hot on some days, but you can handle it.
We used the Orlando FlexTicket and stayed 8 days in the Orlando are. The first 4 and the last 4 days of our vacation. As we had have seen almost everything in the years before we werent in the hurry to experience everything as quicka as possible. We also know we had time enough and could come back on another day, if we wanted.
So we went to breakfast, headed to one of the Parks (IOA, for example). Did everything we wanted to do which had a acceptable waiting-time. At noon when it became realy hot we drove back to the hotel, relaxed and enjoyed the pool. In the evening we went to dinner somewhere and went to another park, as the the weather became nicer, the parks started to clear up. So we could enjoy a park for another 3 or 4 hours.
If it showers really long on a day (an hour+), most people will leave the parks for their hotels. This is a great possibillity to go back into a park. You can expect shorter waittimes.
Keep in mind, that the temperatures go down after a long shower or t-storm which lasts longer than an hour.