EDIT:
TL;DR: HDR brightness won’t help you with non-HDR applications and content (such as emulators). However, most TVs that are capable of HDR also have higher SDR brightness than TVs that lack HDR.
EDIT:
TL;DR: HDR brightness won’t help you with non-HDR applications and content (such as emulators). However, most TVs that are capable of HDR also have higher SDR brightness than TVs that lack HDR.