Flame Sergeant's Spear VS Ifrit's Harpoon

[Frein]

also have to take in consideration that if you die you will lose the sanction buff

Yes but it would also have significant implications for the usefulness of many other weapons, most notably the Garuda drops. I find it strange that nobody seems to have posted any first impressions of them even though many have dropped. I don't have one so I can't try it myself.