So why bother with alternate weapons?

That lasted a fair amount of time into GMS as well, with the level 80+ weapons dropping sporadically until we got Zakum (dropping all level 90 weapons). Specifically the Devil's Sunrise, when BW White Knights were stuck with the Gigantic Sledge (level 70 and slow). Didn't get an alternative until the release of Aquarium and Gobies dropping the Morningstar.

Of course now with Horntail, VPQ and item maker, high level weapons are all about equally available. But the imbalances started a long time ago.