But they will not likely get a spot in the BTC paying signature campaign since manager prefer the users who earned merits in the last 120 days or whatever to apply and eligible for the campaign.
I agree with you, even if someone who get legendary status as airdrop won't be a good participant for a campaign. The legendary member has some advantage when it comes to signature space but that doesn't mean that anyone with such status is also a good poster.
The campaign managers only select the members in a campaign who are active posters and who continue valuable information and their own personal opinion via their posts.