I would define "successful" not only in terms of military potential but also stability and continuity. When one sees how many Seleucid leaders ended assassinated or killed in revolts/wars (just to name Seleucus I, III and IV, Antiochus I, II and III), I side with the Ptolemaic Kingdom.
Seleucid power was more "unfocused" and did not succeed to retain much the loyalty of their subjects.
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