The comment system bundled with Wordpress is not enough for "serious blogging", you'll need plugins to manage spam, allow users to use social accounts, etc. You'll also need plugins for caching. Oh, and you'll need plugins for SEO as well, because the core Wordpress doesn't handle the bare minimum of SEO and isn't flexible enough to allow you to do it yourself. And each plugin expands the attack surface to a system that's known for the persistent attacks, so you have to be constantly looking for updates and keeping everything update. Oh, but not everything, because there are breaking changes. And there are versions that introduce bugs or regressions.

But yeah, a bunch of html pages is over-engineering.

PS: you don't need to use Disqus if you don't want to, there are a myriad of free open-source alternatives you can self-host that will take a fraction of the maintenance work of self-hosting a Wordpress instance.