I think you're mistaken. Signature is usually part of a bounty campaign. The average bounty campaign is usually split into the following: Signature campaign, article writing, youtube videos, twitter retweets & likes, Medium claps, etc. A fixed percentage would be offered to each campaign, and users would receive stakes, and the total tokens allocated for bounty would then be distributed accordingly.
For an airdrop campaign, you could launch it after the bounty campaign, to attract new investors.
Yes i think you are right here. There are more way to prioritized a campaign. Actually is more attractive to everybody as there is low work and so far more people connect it easily. So the more they connected the more it goes to investors. So everything is more import to promote a bounty campaign.