Excalibur(99) has HP proc which outside of aby will average about 350ish at Max HP, on top of this it has Attack+40 and higher DMG than Almace(90). Almace has a Crit WS and ODD which has a much higher proc rate & procs on WSs. Excalibur's HP Proc & 2.5 Damage proc about balances out the ODD of Almace on normal hits, however does not come close on WSs.

This is the place where Excalibur starts to fall, in normal attacks its likely better thanks to HP & ODD not relying on the use of WS like Almace does, and the extra DMG/Attack it has over an Almace. However once you hit WSs, just like Ephemeron it starts to take a dive, its a high DMG weapon with a great attack bonus but the Double Damage can not proc on WSs, the HP proc doesn't effect anything in WS, and the best WS for Excalibur has a killer Attack Penalty. Where as with Almace you have a Crit WS which can be hit with Double Damage making it even more powerful and ends up being good overall. Even with less DMG & Attack the Crits & ODD procs on the WS put it ahead alot of the time.