Yeah, the defiled bosses just take away everything that makes the game fun and turn it into Dark Souls 2. I wanted to see Queen Y, but not enough to suffer through that stupid Amy fight solo.
The bosses in Defiled chalice are more a test of patience than skill, as far as I'm concerned. Never be too eager to get another hit. It took me a while to learn to not dodge when Amygdala jumps, and when the Watchdog was about to charge. As a result neither of them managed to hit me more than a couple of times. Having a rune that increases HP also helps to avoid being killed with a single hit, aside from the Watchdog's charge attack. You can also kind of cheese Amygdala, by staying behind its legs during the last phase. Having a high Bloodtinge, and using a gun like Evelyn with Bone Marrow Ash, will also enable you to decrease its HP from a safe distance. I imagine it'll work with Bowblade as well.
EDIT: A weapon with a good reach, like the Cane's whip form, will also be helpful against Watchdog and Amygdala.
As for the Keeper, the first boss of Defiled chalice, she's very easy with parrying. After the visceral attack, you can just whack her until your stamina ends (if you have a quick weapon like the Cane), and then parry her again.
The first boss of Ihyll chalice was much more challenging for me, despite of not having my HP halved. It took me more tries to beat him than anything else in the game. He's just so aggressive, and has also ranged attacks, so patience helps little there. The Queen is one of my top 5 favorite bosses in the game, and surprisingly easy as well. At least when compared to the preceding ones.
