Just like others said Isshiki has bad stamina, he reached his limit after the fight and hit 0 chakra and needs 2 days to recover.
It took both Hagoromo and Hamura months to seal Kaguya (according anime) and this was Prime kaguya compared to incomplete tentails kaguya that naruto and sasuke fought.
yes naruto and sasuke never fought full power Kaguya (so all statements about kaguya refers to incomplete tentails kaguya) and yet she managed pull ETSB 4-C a feat above JIgen has shown. so i doubt Jigen has more raw power or AP.
JIgen won't keep up with Kaguya for months, since he has a bad stamina.also lets not forget that Jigen had lot prep time before the fight against naruto and sasuke he literally know all about their powers (ninetails ameterasu perfect susanoo etc)But still, Jigen never destroyed sasuke's perfect susanoo, he just pushed Sasuke out of it,
which is nothing compared to Kaguya completely destroying it with god vaccuum attack which is stated a taijutsu attack (physical attack)
https://naruto.fandom.com/wiki/Eighty_Gods_Vacuum_Attack (note wikia got this from databook)
since this a physical attack it means it also cant be absorbed.Jigen has no Rinnegan, meaning Kaguya can one shot him with infinite tsukuyomi.
Kaguya has ash bones and those are real bones which can't be absorbed, so she can one shot Jigen with this too.
Voting for Kaguya, Until JIgen gets his vessel from kawaki (btw Jigen why dont u unseal Kaguya and take her body as vessel? I think with rinnesharingan+ byakugan its better than kawakis body)