The deacon was the result of such a convoluted (and improbable) series of infections and impregnations that it's hard to directly equate it to anything else we've seen. Based on what we saw in David's laboratory, the accelerant throws out all sorts of aberrations, albeit with some underlying, recurrent traits (spider-like infectors, bodily gestation, elongated heads and distended jaws etc).
By the time the crew of the Covenant touch down it seems to have settled into a more stable and predictable lifecycle, involving the spore pods and the neomorph. Even so, they still seemed mindlessly savage to the point that it's difficult to imagine them having a fully closed lifecycle like the xenomorphs.
They're definitely part of the same tendencies in the accelerant: rabid, highly-unstable early phases that gradually coalesce into something more and more resembling the xenomorph we all know so well (as perhaps an inevitable end-point of that cycle), but the circumstances that gave rise to each were too different to say that they are directly related.