Jekyll is also bad lore-wise

I would like to open by saying I'm not attacking anyone for liking Jekyll/Hyde as a character, and there's a good chance I misunderstood some piece of lore or missed some key information that justifies

Everyone who makes decent headway into FGO realizes that they made Jekyll wrong, on purpose, as a joke. He is in the running for, and likely winner of worst servant in FGO (Likely competitors are Saber Gilles, Saber Lily, and Stheno) But if one devotes a little bit of thought, one may come to the realization that, lore-wise, Jekyll is waste of a summon for Chaldea.

Chaldea has to pay the mana cost (being a servant closer to modern day, it probably isn't much, but still). As Jekyll, his only combat application in lore (as I understand it) is that he has a special presence concealment (Powerless Shell) that means he wouldn't get picked out as a Servant... because he's so weak no one aware of Servants would consider it. Compare that to the similarly combat incapable Mata Hari, who has a specialized infiltration ability (Espionage) where until/unless she attacks/gets exposed by her allies enemies will consider her a friend plus her hynotism, Corday, whose noble phantasm guarantees that an enemy won't clock she's about to stab them or the known rare prism Stheno, who also has mind control powers in lore.

Jekyll also comes with the detriment of Hyde, who while usually trapped by noble phantasm activation, occasionally just gets control/summoned and pretends to be Jekyll (As in his Interlude. . I think it also happens in the Shuten Holloween event). Jekyll's skill use quotes support that Hyde has to be actively suppressed. The implications of this mean that one day, Hyde could take over, act like he's still Jekyll right up to the point he decides to stab someone. Possibly someone not a Servant, so he actually gets a kill. Say he stabs support staff. The world is likely gone. They can't be replaced. It's not an acceptable risk. I've never felt that the story implied that Hyde, as summoned in FGO, is particularly strong once exposed. Dudes a time bomb that can't help in the mean time.

Hyde is literally every dark thought Jekyll ever had or will have personified. I don't believe he can be trusted to not want to stab someone, even someone vital, just because. Gorgon can be checked by her sisters. Kiara has Anderson (Plus she wants Guda to initiate). Gilles is checked by the various Jeanes. Lobo wants to save the world in case his descendants survived. Jack the Ripper is focused on the master first, and her/their mental pollution is lessened by Guda's kindness. Kama's been largely disarmed by the power of love. Salieri is focused on Mozart and is calmed by Marie. BB has a program ensuring that humanity has a chance against her grandfathered into her existence. Barghest has alternate ascension lines were she overcomes her curse. Hyde wants to stab someone, and I don't trust a literal dark impulse to be satisfied with promises of future shanking. The only servant I can think of who can't be trusted and can't be checked by prior relationships is Meffy. If anyone thinks of more uncontrollable/untrustworthy servants I'd love to hear them.

I mentioned the interlude earlier, where Hyde lies about being Jekyll to get a chance to stab historical Jekyll. It failed because Jekyll was summoned in place of the historical version and used it as a lesson to Hyde that he needs to rely on Guda. Theoretically, if that hadn't happened, what are the implications? Didn't EMIYA plan to kill Shirou to hopefully cause a paradox to wipe them both from existence? So worst case scenario Hyde undoes himself as a person, best case scenario, he exposed himself to Chaldea, who I don't think are going to take kindly to that. Hyde might be willing to trust Guda, but it feels in character for Hyde to get a hair up his ass, off someone in the night and frame somebody (Probably Meffy).

In summary, Jekyll can't help Guda, and Hyde isn't powerful enough to justify his contract when he's such a flight risk. Thank you for your time