What kind of range do you need to solo bosses?

That covers Zakum, but what about Horntail and Pink Bean? Is it possible to solo them with 50k range? No boss damage.

50k range is enough for HT. Your problem will be survival, not DPS. Leave the Cornians on the bottom alive, their bumps can protect you from 1/1 while seduced.

I don't know about PB.