Alright it's like 3 in the morning and I'm a bit sleepy but it's an interesting conversation. Let me tell you where's the real difference because it's getting more complicated.
First, we should agree that KNX is not a product or solution, it's a protocol and it was done specifically for residential home automation with the option to expand. It's more like an open source OS compared to a proprietary one such as Crestron or Control4 and yes Crestron is, according to every review specialized in HA far superior but that's not the point of the debate.
IMO, Home Automation is not only controlling A,B and C. It's about entertainment as well and that's why the AV solution is very expensive, because you can't achieve it with entry level products.
When I talk about AV processing and streaming, I'm not talking about Plex. I'm talking about 4K HDMI switchers and multiplexers.
I am also talking about multi-channel - multi-room Amplifiers.
Every room has it's own Audio and Video channel. Say you're in the living room watching football, you tell Alexa to switch output to bedroom 1 or you do it from your phone or Crestron remote control.
You can also tell Alexa to turn on the A/C in Bedroom 1 before you join. The audio signal of the channel you're watching is redirected to the speakers in the room you wish to sit.
Say you're playing on spotify, Deezer or Tidal, you can play the music in each and every room or you can airplay / cast from your mobile to the AV processor and get the output anywhere in your house through ceiling / wall speakers etc..
The whole idea behind it is a clean setup. No need for Sat receiver/ Blu-R player etc.. in every room. There's a centralized solution say in a server closet that's handling everything.
In my situation, the AV Processor is connected to two CableVision receivers, Nvidia shield and one BR player; the multi-room amp is connected to an Airplay2 receiver, Bluesound node2i for music streaming and internet radio / FM tuner.
The Video signal is transmitted through Cat6a cables so no need for coaxial cables.
As for the video surveillance, the camera is communicating with the HA through RTSP so the HA app or screens can access the live or recorded sessions, can do whichever scenario you want when detecting motions ( inside or outside ) etc...
I got myself this which is a bit overkill but IMO totally worth the money as it's a replacement for NVR, NAS and server. It's a Ubiquity Xeon server running Ubuntu, it does 4K trans-coding when necessary and has 12 TB of RAID1 storage. Mostly FLAC music and Ripped DVDs
It also has the wireless controller that manages the access points to minimize/eliminate the hand-off.
To Sum it up... if you can give me a product or solution that does :
-Centralized automation using one control point
-Clean integration and simple interface
-Endless customization
-AV processing
-Reliable Direct and indirect lighting control for led lights including dimming
-Complete HVAC control
-Software upgrade and support
i'll be glad to switch tomorrow. People are not stupid to spend thousands if there was the same for less. And no I don't think your argument about the computer room is valid. It's more like comparing an iPhone to a Chinese replica where you need to look for any app you want on the internet so you can download and install it. It's more like DIY vs ready to go.
BTW, KNX is really good and it was a 2nd option but for an all-in-one, I went with Crestron. More expensive but less headache.
Below is a nice article comparing different solutions for lighting only, note that Lutron are pioneer in this field, and that's just lighting :
https://www.customcontrols.co.uk/blog/lutron-lighting-vs-knx-vs-zwaverf/