Every project has a marketing budget/tokens and out of that they use some for bounty campaigns. I agree that it can not be the only mode of promotion and if team relies only on it then bounty hunters will also get less value when they sell tokens on exchanges. so marketing should be implemented by various modes as you explained. also one more important nowdays is market makers and i noticed projects with huge hype got dumped without volume/marketmakers.
as per me even 100k usd worth tokens are good for bounty and if team get good exchanges/hype then this 100k will become 500k usd. win-win situation for all people involved in that project.