Well, we're not there yet, but safe to say that the "some authors" is really just one author: Nick Sekunda. Sometimes I agree with him, other times not. In this case, as do many other historians and reviewers of his books, I think he is overstepping and drawing big sweeping conclusions with too little evidence. Bear in mind that the Successors were using chain mail and ovoid shields long before they came across the Romans. Furthermore, there is no evidence for the adoption of the pilum and the spear was still the primary weapon. At most, I think it can be said that the Successors might have adopted some forms of Roman deployment and organization on the battlefield - although with their own twist - for their thureophoroi and thorakitai. It is true, however, to note that the great phalanx disappeared from the Ptolemaic army sometime after Panion, which may have been due to the big losses there. The Seleukids are noted as using a phalanx in the Jewish revolts, but it could be argued that phalanx was a general term meaning any organization of men.. Even then, if you're willing to accept the complete disappearance of the phalanx, we still see a Hellenistic fighting style.

Of Numidia and Pontos, I have to do some more readings, but I think that was pretty cut and dry and that they were done in imitation of the Romans. But I've forgotten so much about them that I can't say for sure. I'd have to do some research on them to say for certain what we'll intend on doing.