They get hot, even with the vents open. I just took some measurements... vents closed all day, 72 outside air temp, 113 inside top center, 78 on dirt surface of 5 gallon bag. I dont know where you measured, but hotter temps up top can be slightly misleading. Misting the floor brings down the temps when it gets really warm.
I look at the tent as a season extender. Allows for dryer warmer start and finish. Not the best for hottest days in my area. My plants are outside the tent as weather permits. The tent is awesome for those unexpected thunderstorms, hail, heavy winds, etc.