@OP Keep in mind, that's not 10k in damage dealt, that's 10k to attack rating. With that said, the upper bound on attack you'll see in a typical rich-people-but-not-named-agelia party is around 15k; they barely hit the attack cap on Klaus, who has 5036 DEF.
What's confusing is how this affects Scythe the most. In terms of percentiles with skill modifiers, Loom is 0.26, Thread is 0.28.
In comparison, Butterfly Swing 1st hit is 0.289, subsequent swings are 0.22. Stigma, oh boy.. that's 0.42.
Staff has their 0.38 Firebolt and 0.41 Ice Spear.
Amaranth Kick, 0.27.
Lann has their 0.19 + ~30% = 0.247 Gliding Fury.
Everyone has their high-burst damage attacks. Source
http://vindictushq.com/index.php?/topic/9430-new-damage-tables-out-12b-and-12c/; I realize it's probably a bit out of date but I highly doubt the numbers have changed significantly so much so that my point is nullified. If it hurts scythe, everyone's hurt. And I don't even think anyone is hurt in the way you're thinking.
You couldn't argue that Loom and Thread go hand in hand, giving them a sum percentile of 0.54, because they're still 2 separate hits.
Back to the attack cap, hardly anyone hits it on today's raids. When's the last time you've seen someone with 17k attack? How many do you see?