I'm a fair bit larger than average and I have had a lot of WGs comment on my size, mostly positively but in some cases as soon as they've seen it they've said, jokingly, they're a bit scared and to be careful and gentle as when she's shagging multiple blokes a day, well hung guys tend to stretch them out and leave them sore. As with many things in life, some women will love and can handle a large cock others don't and can't.
Don't think I've ever heard the cliché: 'it's so deep!' gasped in a fake manner but most women have told me it feels very nice to be completely filled up to the point where I'm bottoming out against their cervix. Some memorable comments I've received whilst fully inside are: 'you fill me up perfectly' and: 'they should make toys of you!' Of course for some it's straight up not pleasant and certain positions (doggy is bad for this) are just not doable comfortably for her with a large penis. I've asked them about this and most say that whilst being 'bottomed out' in feels very satisfying, if I accidentally crash against their cervix going too deep too hard that hurts and is not pleasant, feeling like they've been punched in the stomach. I find many of them who struggle to take me and can't manage doggy enjoy cowgirl as they are in control of depth and speed of penetration.
I've no doubt for some this saying is indeed just a way to be kind to the punter and get them turned on and out the door quicker but from personal experience, many do enjoy deep penetration but you obviously need to be careful and not all will enjoy it. Having a larger than average penis doesn't automatically a good lover make and a well hung bloke smashing away with no regard is unlikely to leave the receiver a cum drunk mess and more likely in the foetal position feeling like she's been punched in the stomach.