Is PDR Usless for MErc

This is true but in most cases, you decide between %ignore and %boss. If you had a choice, a mercedes should take %boss. Defense break is sort of useless on my mercedes right now though as in it doesn't provide that much help.

30% leafre set
21% spikes royale + combat order
30% ignore on weapon
15% ignore on arrow from nebulute

Total: 96% ignore def

You forgot to take into account your Ambition.