A question about crafting a bow

hey guys,
new ranger here..

Ive read some crafting guides and saw some youtube guides about what is the best way to craft a bow (end game)..

I got a question for you.. Ive seen some guides saying you should get Harbinger bow (ilvl 77+-) and hope for atleast 85%+ on pys dmg once you trasmute it.

isnt it a bit low? for my understanding, this way allows you to get max of 90% pys damage, but ive seen bows with over 120%, so why is considered good?

thanks!

p.s
a link to a good guide will be most welcome