If the best exposition of the 'Legion vs Phalanx' debate is to say it is a waste of time, words fail me. It is perfectly possible to isolate organisational and tactical factors from those others mentioned by Xenophon and thus pass judgement on the two systems; though I would agree that other factors have alot to contribute to success in battle, generalship is about using the tools one is given and if one wishes to pass judgement on the generals of antiquity one needs to consider the capabilities of the systems used by their forces and the enemy.
Yes, no Hellenistic kingdom went over to a wholly legion system, but the reasons are not hard to find; the Seleukids had ceased to exist as a major power 24 years after Magnesia, and the Ptolemies, as Roman allies, could call on the real deal rather than energetically reform, in both cases internecine strife destabilised the state.
But to all those phalangophiles, clinging to their dreams of victories unwon, I pose one question, can a phalanx fight in woods, mountains or even on broken ground? The answer is no. This does not mean that the legions were forever victorious, even against phalanx armies, Asculum and Beneventum were defeats but thereafter there may have been a couple of stalemates but the picture is one of unbroken defeat for the phalanxes (Kynokephalai, Pydna, Thermopylai, Magnesia, Korinth, Orchomenos, Chaironaia, Zeleia and probably more).
Given this, the question arises, why did the Antigonid phalanx put up so much better a show than the easterners'? Magnesia was good phalanx ground, it may well have been the same site as Korupedion in 280BC. The answer probably comes down to morale; the phalanx failed to attack because it lacked the 'will to combat'.
Ages back in the thread someone suggested that the story of the Greeks being shocked by gladius wounds was Roman propaganda due to Livy; I don't dispute that this is certainly possible but I would like to point out that the scenario is a very Hellenistic one, viz a general whose strategem backfires, Polybios was no fan of Philip V, so it is equally possible that Livy found the story ready made.
I do agree that the debate is frequently otiose with people adducing wargames rules as evidence! Some twit once suggested that because he had defeated a Norman army re-fighting Hastings by charging off Senlac ridge with the whole Saxon army Harold II would have won had he done the same, the result would actually have been to repeat the destruction of those Saxons who did pursue the Bretons on a larger scale. However, it is a worthwhile exercise when conducted with reference to the actual evidence; this is, after all how military systems change (not always advance

I'll get back on the Pontic campaigns, though I dare say Xenophon will beat me to the punch.