You’ll end up a lot more satisfied if you stop focusing on HomeKit. There are a lot of great products out there and HomeKit should be a non-factor if you want the best, full featured products. If you want overpriced, limited selection, limited features...stick with HomeKit.
I agree with you to an extent but do you have an example for clarity?
Where I don't agree is where the goal is convenience and your eco system is Home Kit ready. For my example I'll use a light switch (or outlet..whatever). Since I have an iPhone, Apple Watch, Mac and HomePod saying "Hey Siri turn X light on/off". Could be any devices though, "Hey Siri set them temp to 72".
Grabbing my phone, unlocking, opening an app, lettings it load, activating a function, is only more convenient if the light switch/thermostat isn't nearby.
Another example is ease of use and reliability with geofencing. I prefer not to have 5 apps using my exact location GPS compared HomeKit that is baked into the OS.
Where I agree with you is when you are forced to compromise. Security cameras is one of those places however even then I would still strongly recommend someone do a lot of research on how their data is used. Also use no name cameras outside, never looking at you especially in a bedroom or someplace private.