We've been rendering images in SDR forever, and most people don't have HDR capable hardware or software yet, so I don't know how you could consider it as broken to render the image without the HDR data?
I’ve seen countless of issues where you place a PNG logo on top of a css background:#123456 and expect the colors to match, so the logo blends in seamlessly to the whole page.
On your machine it does and everything looks beautiful. On the customer machine with Internet explorer they don’t, so the logo has an ugly square around it.
95%+ of humans won't even notice HDR being missing. Everyone with eyes will notice a black or white square.
For this particular use case, yes, transparency is more suitable than trying to match.