I definitely agree with this statement.
That’s why for my own setup (not very large… 40 Switch actuator channels and 12 Shutter actuator channels), I didn’t go the DIY way and I bought the GIRA KNX/IP Router. There are many manufacturers out there. One good option is: MDT
George’s list is more accurate also. The items 1 & 3 in my list are basically a “DIY / home-made” KNX/IP gateway.
The KNX/IP gateway can be either a standalone device (like the GIRA) or a “construction” of hardware (TPUART+Raspberry) and software (knxd) components