o come on. No software is perfect. It is guaranteed that there always is someone whose setup will get yanked at some point. The root cause isn't always the iOS update itself. Since Homekit can have so many different brand devices and ways that they connect, there's always a combination of devices possible that has problems.
I borked a few rules myself by editing them in the wrong app (Home app, Eve app or Home+ app). And a couple of versions back I had issues with Homekit where some buttons (not all) randomly reacted extremely slow or were sometimes completely ignored. It turned out to be an Hue bridge issue that surfaced when the new HK version rolled out. I had to reboot the Hue bridge every few days as a workaround. It was network bug that had to be fixed by Signify, not Apple in this case.
What I've seen so far is that for many wifi devices the trouble is related to the AP being used. Bad range or incorrect handling of the mDNS data. I use Thread now and that proved to be much more reliable than wifi.
Now version 16 has improved the response time for my setup. Quicker and more consistent. The fact that I recently added a couple of more devices and rules, didn't slow it down. It still works, even the more complex rules.