That's not really a good thing about HDCP at all. Not only that, I certainly have bad devices supporting HDCP.
In reality, HDCP causes issues with DisplayPort and HDMI link by being one of the weakest links (HDCP signalling is usually the problem in long or cheap cables). Any issue makes HDCP kill the connection and renegotiate content protection, which takes time where there is no content.
We still to this day have trouble with SCART-like features. It's just now called HDMI-CEC, and is very much a hit-or-miss scenario, even within the same brand. Case-in-point: I have an older Philips Android TV, where CEC in my setup works fine. The same setup does not work at all on a slightly newer iteration of Android TVs from Philips, despite both running a similar Android Oreo build.
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Also note: The default for SCART was composite, with optional S-Video and RGB support, and very rarely, component (which quality-wise would be somewhere around RGB). S-Video was the common "quality" setting that "just worked", which is close enough to component (and thus RGB) in quality for the material of the time.
Plus, getting suboptimal image is not as bad as getting no image at all, or missing features. HDCP and CEC is arguably a huge downgrade from SCART in that regard.
... this comment is longer than I intended ...