Right? At this point I'm just sticking with WordPress because I can't be bothered to migrate a bunch of sites off of it. Every year for the past decade it's felt jankier. Tumblr's backend has to be a dumpster fire for this to seem like a good idea.
My criticism aside, WP still has the convenience factor of being the open source web platform that has a plugin for just about any need. Whether those plugins are gonna break for site or introduce interesting new vulnerabilities is a different discussion.