Also many balanced headphone outputs will be damaged if you connect the L- and R- pins to use with a normal TRS headphone cable set. This is because the outputs are in fact balanced and not tied together. thus there are separate amplifies for units with both output types. probably why a different connector size is used so there will be no accidents. TRS to TRRS adapters are of course not an issue, but the other way will likely not be a good outcome.
Some brands do support TRRS in 3.5mm output too, I think FiiO BTR3 and Oppo HA-2 had this ruction - at least it worked for my custom made TRRS 3.5mm headphone cable. but how it was internally amped I am not 100% certain.