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 Legandary Rank is just a Rank as any other Rank , it only shows others in the first way that you longer on the Forum as others.
If you a good poster or a shit poster dosnt care , there are still some shit posting Users that are more usefull as other Users.
Ranking up just for getting a better spot in an Signature Campaign is still in my opinion the wrong move and idea to be good a User.
When the Merit System was implemented i got the Hero Member Rank and at this time i wasnt in any Signature Campaign.
It depends all on your opinions and what you want here on the Forum.