Yes the issue is and is always been how CA's interact with the copyright license. When code is BSD or MIT licensed, it is difficult for CA's to give any party an advantage over another. Not impossible but certainly difficult.
But when code is (L)GPL licensed the terms of the associated CA can change the playing field drastically and can be a significant barrier for projects that should be co-developed by people and entities which have their own business interests to look after. A CA which allows one party to proprietary relicense gives that one party a significant business advantage over other parties. In the calculus of business dynamics that is easily viewable as a situation to avoid. It also allows one party to financially profit from the contributions of others without any equitable trickle back. This can be viewed as taking unfair advantage of cheap labor for financial gain by a for-profit entity. Those who argue this is okay are deliberately devaluing the contributed labor and utterly misunderstand how the FOSS ecosystem works as a marketplace which builds _value_ into the commons.
That being said CAs _can_ be done in a way that nullifies these concerns. The devil is in the details, and the Harmony language I don't think goes far enough to express that level of detail necessary to make the proprietary options reasonable.
If a CA has strong promise back clauses or liberal re-licensing clauses which engage if the central authority oversteps prescribed limits of its proprietary re-licensing authority then a CA can be a reasonable compromise between the interests of the central authority and contributor interests.
The FSF's evolving promise-back language in its CA tries very hard to mitigate the unfairness inherent when a CA is used with (L)GPL code while still giving the FSF the authority to re-license in good faith to meet its foundational objectives without giving any single entity a marketplace advantage or taking unfair advantage of contributor labor. I believe Harmony's draft language has an option that attempts FSF like use of a CA which explicitly does not include proprietary licensing.
And I think Trolltech's CA that was used with (L)GPL'd Qt in the past also made a reasonable attempt at a compromise concerning proprietary licensing. I don't see the Harmony draft language covering this case at all. I don't see any language in the Harmony draft that puts reasonable compromise limits on proprietary licensing of contributed code.
The old Trolltech CA used a non-profit entity structure as a sort of code escrow authority. If Trolltech stopped shipping the open licensed code, and made it available only as a proprietary option, a clause latched which permitted the non-profit entity to re-license the code as BSD which anyone could then turn into a proprietary offering. This did give Trolltech a marketplace advantage as it gave them sole ability to make proprietary licensing deals. But that advantage only existed under the condition that they continued to provide (L)GPL code. If they got greedy, the BSD relicensing doomsday clause kicked-in allowing new vendors to compete in proprietary offerings without TrollTech's blessing. Not perfect, but definitely a reasonable compromise to restrain future corporate bad faith activity. But it doesn't solve the problem of project co-development by multiple business entities in the same way the FSF's use of a CA does.