Something clicked with me when I came across htmly. It made perfect sense for the future of my writing. So I wanted to make the move ASAP, and here we are. I only did a cursory look into these flat files CMSs, and installed and tests a few of them, so take these thoughts with a grain of salt;
htmly: abandonware, it’s no longer actively developed. Doesn’t look good out of the box (and none of the available themes are particularly good).
Grav: very powerful, too powerful. The only one (that I’ve looked into) that can be setup without dashboard / admin site. But, it’s a bit tricky to setup as a blog because file structures is needed for these flat file CMSs, blog posts are a bit cumbersome to manage as flat files.
I’m not a fan of the admin side, reminded me a lot of the complexity of Wordpress. There are these “skeletons”, it’s kinda like this premade sites to get you up and running faster, but that just screams finicky to me.
Kirby: read good things about it. Not free, so a pass for now.
Bludit: perfect for my case, see that bolded text on my previous post about tumblr? This is exactly that. Dead simple blogging system (it’s not a platform), add new page, write in markdown, save, bam a new blog post. Looks good out of the box, but I’m using the micro theme (modified it so it's slightly larger, and I'm calling it Mini -- which I may or may not release it, no promises).
Pico: haven’t installed this one, since my heart is set on Bludit. It seems more capable than Bludit, but not as complex as Grav.
I’m really liking these flat file CMSs. Like, mechanically simple, yet robust. They can't do any of the tricks with database like left join etc. Do we really need those features for blogs? The contents are files so the search function will be on the terrible side, but we have google for that. Even with database you'll likely to roll another indexing engine to have a better search anyway.
Seriously, look into these flat file CMS, it may be perfect for your next web project.