On another hand, after reading some articles a while ago that mentioned security issues surrounding smart bulbs (when it comes to selling them to someone after using them in your own home due to some persisted settings), I bet that your theory could be correct as well.
The Phillips app is so junky I just use the hard power switches somewhat frequently.
https://huehomelighting.com/new-power-feature-to-retain-colo...
Their lights work great with HomeKit, as well as many other devices do. So instead of having a separate app for Kasa switches, app for Hue, app for LiFX, and an app for Nanoleaf, I can control them all straight from HomeKit. Considering that this is easily doable, it seems totally possible to do this with something other than just HomeKit as well.
Ehhh... I can't speak to the rest of the HomeKit integration but the Siri stuff isn't so great either. First it required upgrading the hub, it still only works with Philips bulbs (even though the Hue can control other smart bulbs like IKEA whatevers). After setting it up I still get "device not responding" responses from Siri at least 1/5th of the time.
Using a different app would potentially improve the problems between the hub and phone, but not between the hub and the zigbee devices.