First of all, that parable wasn't correctly explained, "a man's food, is another man's poison" simply means that, what one man rejects or finds unappealing, another man may so much love that thing and totally embrace it as if his life is tied to it, this is a bit different from the way you explained it that, what happens to a man, another man may benefit from it.
Anyways, first, I will partially agree with what hugeblack said, and based on what I think personally, I do not think that the ban of or on mixers promoting their services on bitcointalk, and the mixers coming on this forum to promote their services, will automatically take this forum to the same level that bitcointalk currently is so as for the both forum to start contending with each other as to which will be greater, remember, bitcointalk has a backing and will continue to enjoy its first mover advantage.
For altcoinstalks to atleast, get the kind of traffic bitcointalk has, it's need promotion, mixers alone coming here will surely do something but not much, altcoinstalks need to be promoted all around the crypto community.
Trust me, bitcointalk didn't just become big simply by allowing signature campaigns, it was promoted, though indirectly, for example, discussing about crypto in WhatsApp or telegram groups and sharing links to posts on bitcointalk, even some news houses referencing some posts on bitcointalk in their news articles - this are the indirect promotions bitcointalk enjoyed and still enjoy till date.
We have to make the same start to happen for altcoinstalks, this is how more people will get to discover this forum and the traffic will grow over time.
And when the traffic grows, even more businesses and services will be w willing or eager to come here and promote their business or services, they won't have to wait until they are banned from promoting on the other forum.