Depends what you mean. I HATE grinding but stories that rush straight into the sex are also unsatisfying. Having things nicely paced with some story buildup to each LI is the best.
In studies where participants were measured by researchers (not self-reported), the difference in average penis size between men from the US and Japan was found to be +0.02 cm (US).
While there certainly aren't any Mandingos in Japan, from what I understand, the size of the dicks in JAV are usually due to the preferences of the actresses. They have a lot more control over their scenes than pornstars in the US and are able to specify what they are comfortable with and what...
For me, realism is relative to the general silliness of the story. If it's super serious then realistic behavior is required. If it's just for laughs, do whatever you like.
I'm fine with it as long as it's not too out of nowhere like a random fuck of a stranger. That contributes nothing to the plot. But, giving you a sex scene with a more minor character that had some context is fine.
Is your partner having sex in front of you with someone else an event that's common enough for it to have become such a regularly brought up topic? I'm genuinely confused as to how this became a thing to even talk about. To me, it seems like worrying about leprosy. Sure, it's a thing that...