Having lived for many years in the midwest, and now living in the (on the eastern edge of the) southwest I'll offer my opinion.
Yes, I would say it's really freakin hot. That said, I don't think it's as hot as you might think, with you're body being acclimated to what the "feels like" temperature of summer humidity at 65% to 80% is.
I think that a fair comparison is 104 degrees and 5% humidity in Phoenix equals 97 degrees and 40% humidity in Dallas equals 92 degrees and 90% humidity in Jacksonville, Mississippi. In other words, those half dozen days a year in Cleveland that are 90 degrees and 95% humidity are what the entire summer and several weeks of both the spring and fall feel like in Phoenix. That said, no miserable 5 months of winter. Just a few cold days.