ABR is absolutely required for distribution. MoQ also supports ABR, but additionally gives you the ability to also drop the tail of a GoP if a rendition switch is too slow, or no lower rendition exists.

As for maintaining existing standards, it depends on your goals. If you're not trying to push boundaries then absolutely, HLS/DASH is great for quickly getting off the ground. But if you're looking for something in-between HLS and WebRTC then MoQ is compelling.