This is going to sound harsher than I mean it to, for which I apologize in advance.
If artists are going to be upset that their art is sealed away by their bosses, then they should probably be their own bosses. IP is "Intellectual Property." If you believe that the artist should be the sole arbiter of whether it's available and how, I am not necessarily against you. However, in that case, the artist can't really get paid to produce it.
As well say that mechanics are being treated unfairly when a car owner has them fix up his car and then puts it in his private garage.
Artists who are paid to produce art for their bosses are creating a product. They are creating IP that is owned by the person who paid for it.
I suspect you'd be just as upset if Matt Miller had personally produced everything in CoH, and then he decided to shut it down. Or if Micheal Jackson, on his death bed, demanded publicly that all copies of his work be destroyed, that it might die permanently with him.
IP laws exist to allow "intellectual" works - works of art and creativity - to be assigned value in a meaningful way, so that those who create it can use it to support themselves and be encouraged by the desire of others to expend their resources on supporting them to continue to produce more. They exist to transform "ideas" in the form of their execution into products which can be bought, sold, and owned.
It may well be that "artists' bosses" are all evil corrupt monsters who abuse them like slaves, but if so, that's just a sign that artists are, for whatever reason, willing to put up with that or are unable to achieve greater reward for the value they produce. I'm not saying laws as written are perfect, but I am saying that it is very dangerous to the actual interests of artists to muck about with laws naively. Good intentions pave hell. Be very careful to consider what artists are paid for that they lose control of IP under current law, and whether they could find work doing that sort of creative production under whatever system you propose.
I'm fond of moving as much towards direct-marketing of art and the like as possible; it does mean there are fewer middle men taking a cut of what people will pay artists for. However, there are still many things production and publication companies do: marketing, venues, resource acquisition and management... all of these things are expensive and can give new artists a huge leg up. The exploitation that infamously occurs (real or fictional; I honestly don't know) is not something laws prohibiting IP transfer would fix. It would just change the shape of it, and make it harder for naive and inexperienced artists to "break in" to anything because they would know less about how to sell their product.
