No, I'm sure you're correct that mainstream economics incorporates ideas from outsider economists, rather like how monopolists buy up competitors. But there are different kinds of incorporation or co-optation. I'm familiar with this syncretism in the case of the history of religions, but it's apparent also in how mainstream culture co-opts countercultures. Often this happens as a kind of bastardization that neuters the implicit criticisms. Centrism in that case becomes propagandistic, a political compromise or fig leaf that covers up a deeper incoherence or unsavory agenda.

So yes, neoclassical economics has ballooned into an unfalsifiable collection of models which now lacks a clear narrative and over-arching theory. That's to say mainstream economics looks more theological than scientific. Remind me again how this is supposed to help your case.