Based on the science we have training to failure is optimal for hypertrophy. The thing is I rarely see most pros train to failure. Didn't dorian train to failure on just about every set?
Personally I have always made my best size gains in the 12-20 rep range. My best strength gains in the 6-8 rep range. Then again if you look at Olympic lifters they have huge huge quads, spinal erectors, and often very well developed traps and delts but rarely do more than 3-5 reps during their training.
I also find it hard to believe training a muscle once per week is really optimal especially for small bodyparts like biceps,calves etc which often recover in 24-48 hours.
My coach rarely trains me to failure. Instead, he often has me train to the point where I can't keep good form on higher rep sets. On low rep sets we stop after only a few singles or doubles (with long rest periods in between).
If your goal is hypertrophy, I am guessing you should do direct training of biceps, calves and other small bodyparts, one to two times per week maximum. Don't forget the biceps get trained when you do compound exercises, like clean and press, deadlift, pullups, etc. and calves get trained when you do compound exercises like squats, deadlifts, etc.
For strength training, my coach recommends against direct training of biceps or calves. I train them anyway because I don't want to be the strongman in the room with small biceps and triceps! My calves grow without direct training so I don't do them. . .