Situations that are less favorable for maintaining AM3, and situations where you are not receiving proper accuracy buffs are where Upukirex will come ahead. The dps on Upukirex is close enough to the dps of Ryunohige with AM3
active to make it a serious contender once you factor in the additional time required to maintain AM3.
The ability to use your spirit/soul jump at the end of AM3 to quickly boost your TP favors Ryu of course. However,
in situations where maintaining AM3 is unfavorable, I have no doubts that once you take the polearms off of paper and start actually using them, Upukirex will win. The real question will come down to, "Just how much wiggle room do I have with how long it takes me to refresh my AM3 in order to keep Ryu ahead of Upukirex."
That being said though, for the time being at least, if you aren't currently capable of making a Ryu, you also probably aren't capable of getting an Upukirex unless you buy a spot in a bee win for loads of gil.