If Albedo was the strongest of the guardians, how come she didn't stand a chance against Shalltear? It seems SHE is the strongest in fact, considering Ains had trouble and all guardians needed to team up against her.
albeido is a full tanky dps type, more in line of being an absurd soak tank, imagine a tank with 99% damage reduction.
where as shaltier is a hybrid knight mage with unholy property, and even more so can absorb health.
so imagine a full tank fighting a life-stealing tanky mage.
shaltier can't kill albeido because shes too damn tanky, where as albeido can't kill shaltier because she'd just steal back health.
they'd both be in a stalemate for pretty much the entire time, even ainz took quite a bit of effort to get her health low enough to kill, and hes a pure nuke mage!