Simon.
you make very good points, and i always value highly your input on studio tech.
i had similar feelings until recently , when i came across a series of you tube videos where a guy called julian krause does rigorous testing on various inexpensive audio interfaces.
he tests in detail with charts and measurements. etc etc.
thus i came to the conclusion that the latest generation of interfaces are getting very good these days.
check a few out.
focusrite scarlett
https://www.youtube.com/watch?v=Jg6RZZBS9lsmotu m.2
https://www.youtube.com/watch?v=D3ednXYd1pAmaudio 192
https://www.youtube.com/watch?v=R-q41YOSl_Qmy evo
https://www.youtube.com/watch?v=RrAdO8n8cfUand there are many others simon includeing behringer reviewed.
https://www.youtube.com/watch?v=U_SRRhXnPrAheres his channel on you tube
https://www.youtube.com/channel/UC0HrD4cTsQpAZ8KK9jPzzGga slew of reviews and measurements.
best
muso.