although the bounty hunter will be paid after 3 months since ICO ends and investors will be paid in several batch but this has no positive impact on OIO prices on the market so I think this strategy is useless
although this strategy has proved useless but some ICO dev have always blamed the bounty hunter as dumper

blaming the bounty hunter for dumping problems doesn't seem right. because basically the allocation for bounty campaigns is very small compared to the total tokens used for sales bonuses. they should not give a big bounty from the start if they don't want to be dumped.
Yes, I really agree with you. If they only blame the bounty hunter, I think it is a big mistake for them, in my opinion this ICO if there is no bounty hunter they will never succeed in selling their tokens. Is it possible that their tokens do not have a future so they reason to fear the dump of bounty hunters. I think if their tokens are good they don't need to be afraid of dumps, surely everything will be fine.