All it does is make enemies sword sponges. I'll pass.
This.
The only time I play on master is with my Altmer archmage. He has Destruction, Conjuration, Illusion and Restoration all at 100 and only has perks in them, and boy is he overpowered. It's too bad he's a good guy, though; I'd really enjoy making him a vampire lord.
For you Master players out there that are werewolves, isn't the problem of being underpowered even more evident on this difficulty level?
Nope

While I agree with the notion that werewolves ought get a perk tree to balance them with vampire lords (and I'm excited for it, too!), they were powerful enough in vanilla. People tend to have a hard time playing them, but as far as I'm concerned, if I can manage to excel at high levels as a werewolf, anyone can--an inability to simply means it's not suiting your playstyle.
Werewolves are all about mobility and DPS. I've had the most success as a werewolf as a typical Khajiit rogue: Light Armor, Sneak, and dual wielding 1H weapons. In my humanoid form, I developed effective combat tactics that helped me stay alive and well on the battlefield as well as keep me potent, since I was lightly armed and armored. Werewolves are similar, having a pair of claws that strike very fast (and unlike humanoids, werewolves don't suffer a speed penalty with the left claw and in fact strike fastest by alternating claw swipes), an extra 100 health and stamina, incredible stamina regeneration, and blinding speed--werewolves can run faster than humanoids can sprint and can sprint faster than horses.
Thanks to their similarities, my rogue tactics transitioned extremely well into werewolf play. I knew how to dodge many enemies and could predict almost all enemy attacks properly, from animals to giants to trolls to mages and even different weapon styles of NPCs. The boost to speed was an incredible boon, as well. On top of that, werewolves can launch everything right up to and including giants like rag dolls with their power attacks and sprinting attacks, and can stun mammoths and dragons with those same attacks. And all of that is not even including the totem powers (werewolf "shouts," if you will).
That's just it in brief, but I'll gladly explain my werewolf tactics in detail to anyone who wants or needs to know how to effectively utilize the beast form. Contrary to popular belief, it's perfectly viable even at higher levels (40+) and on master.