Yeah, to your point, I think 50% of the orgasm or more, for many women, is mental. I wonder how often people who report their wife cumming like crazy on a bigger cock is primarily just their wife being extremely aroused by being with a new partner and the naughtiness of what she's doing. Nothing dampens lust like familiarity....
My wife hasn't been with another partner yet but, being over 40, she's recently started to have trouble cumming. I used to make her cum at least 2-3 times, every time we had sex in our 20s and 30s... now if she's tired or has been drinking, even 1 can be a challenge. I've tried bigger dildos, which she doesn't like that much as she gets sore quickly, vibrators, which work sometimes... what never fails though is porn. She never watches porn herself but if she's having trouble, I give her pornhub on the tablet and once she finds something she is into (usually a wife getting DPed lol) she's always able to cum.
So, while I imagine a bigger cock could be better in some ways, providing more feeling of fullness, I think a bigger part of it is mental.
It would still be fun for me to watch her take a huge cock though haha...