I do not have an issue with what you have stated, I broadly agree with your comments. What I fail to understand is why there was no plan but the bounty manager to cover unforeseen circumstances (such as high transaction fees and/or loss of token value) because the participants would rightly expect to receive what they signed up for.
Well, we can't make this excuse that since there were all newbies in that campiagn , doing the spamming, therefore they should not be paid the token or paid less than what was promised to them earlier. Also, this excuse may not work that most of the newbies might be alts of each other and hence do not deserve the tokens.
The right way to treat them was to exclude those whom they think are the alts of each other and never let them participate in the campiagn. If it was difficult to detect the alts, they should have made a rule of not accpeting the newbies in the campiagns at the start. Similiary if the posts done were spamming, why not excluded those particiapnts initially from the campiaign.
Get all the social meida activities and promotions and then making these spamming / alts excues, is just not right and shows the project does not want to pay for work.