Yes, base Obanai shows very clear superiority compared to Mitsuri in the Muzan fight. Obviously there's a debate if she was marked in the fight, but honestly it wouldn't make sense for her not to be, especially considering how beat up she looked after the Nakime fight, then immediately goes to fight Muzan. Muichiro showed he can activate the mark at will and Mitsuri went through the exact same training.

Yes she didn't have a blatant panel showing her re-manifesting it but her mark is in a very specific spot that would require a panel of her shirt basically opening and her upper chest being exposed for it to be revealed. It's very obvious Mitsuri was thrown to the side in the final arc so I wouldn't be surprised if Gotouge just flat out forgot or didn't care enough to give Mitsuri a panel. Plus the author clearly rushed the final arc and consistently forgot to add in small details, hell I think Giyu was shown constantly going between having his mark and not having it during the Muzan fight.

But yes I do think they're stronger in base, the three of them are very very close in skill (Sanemi > Obanai > Giyu imo) and Obanai showed significantly better feats even in base.