Ooh a good question. Reflecting back on why HTML sitemaps were a thing, they were generally used as a way to help users overcome dead ends.
Basically, if a user got stuck they could always go to the sitemap and hopefully find their way from there. As sites got bigger and bigger, so did sitemaps, making them terrible at achieving their original goal. Then came of the phase of having a sitemap that simply listed all the site pages which really was little more than an SEO trick to try and get all pages indexed and again provided vary little value for users.
That fact is you shouldn’t need an HTML sitemap. It’s fine to have one and if so, it should be well structured and informational, but there are no real pros or cons.
You could argue that if lots of people are visiting your sitemap your information architecture must suck. People are obviously getting lost and not finding what they want so there must be a problem with your user journey mapping and likely your navigation.
One reason for having an HTML sitemap might be to actively monitor where people are clicking on it from so you address the why, although generally most sites now have a search function that is more likely to yield valuable data.
So, my take would be whether you do or do not have a sitemap, there are no obvious pros or cons. If you do, just be a bit more imaginative that listing all your page titles or recreating your mega menu in text form and don’t have it as a DEFCON 1 urgent priority.