Please tell me, if I am wrong or missed something.
You missed that the only reason the bounty campaigns care about rank is that it gives a bigger signature space with more styling options. theymos also removed links from Jr Member accounts just before bringing in the merit system. They're not going to pay people to advertise if they can't even put a link to their site in it.
Yes sure, theymos can remove links from members but bounty manager can pay the members as per his/her will. There were many campaigns where jr. member/member and full member/sr. member had same payout.
I don't follow bounties so I have no idea but it seems odd that anyone paying for advertising space would not take into account the visibility impact of that advert when setting pay rates. It's certainly the case in all the Bitcoin paying signature campaigns. Also, none of those campaigns accepts Newbies because they could not have links. By extending this to include Jr. Members it in effect means an account must get a minimum of 10 Merit to be a viable proposition to any advertiser.