That is ridiculous - you wouldn't carry the weight around for that power level for such a short flight segment need. If you are averaging 35% power you have WAY to big an engine in your plane!!
They might use that fact to oversize them giving better redundancy (eg. one can fail during takeoff and it not be an issue).
Yep. I lived in Truckee for awhile, and the local airport there is notorious for pilots making "unexpected landings" into the mountainside right after takeoff because they didn't climb fast enough.