you don’t need thousand hour for that,
once you unlocked a mercenaries, you can farm their coin for 10 coin / 3 minute
100 coin for 30 minute
1000 coin for 300 minute (5 hour)
2000 coin for 600 minute (10 hour average time for 1 max out mercenaries)
(this is average time for robotic style non stop gameplay)
and also you don’t really need to max them out for pvp :
read my post below,
disagree with what i said ?
feel free to tell me your perspective.