Outside of game terminology, 'arcane' (in its magic-related meaning) and 'occult' are basically synonyms - meaning magic from secret lore, while 'psychic' (magic from the mind) and 'occult' are not. Shouldn't arcane magic be what is 'occult', and not psychic magic?
One thing confuses me though: Lots of rich folks getting killed, but no mention of raising the dead. There may be restrictions on it in the oriental setting, perhaps a law against raising the loser of a duel for one, so it may work, but it seems like a big plot hole that should at least be explained. Thanks :)
On the original question, why don't you make them roll the stats using a method that doesn't produce really high ones too often, but allow them to roll up a new set if the total of their ability modifiers is too low? Set the cutoff a bit below whatever the characters you think are balanced have.
I wouldn't necessarily have a problem with any of those, as long as it's done well. There's nothing wrong with using the classics once in a while.
What I have a problem with is "Stop the summoning", where the PCs have to stop something (often not specified beyond "Use something with an epic CR") from being summoned by mad cultists.
I don't have many issues of Dungeon, but I have #114 (the one with Mad God's Key), and all three - all three - adventures in there use this plot device. Many of WotC's free adventures seem to use it as well. This is particularly bad because if world-ending summoning attempts happen so often, like in every single place the PCs happen to go, surely they must happen when the PCs are not around something like 100 times a day around the game world.