changing my mind on webm (we'll see about webp) but the filesize difference between two identical video streams in mp4 and webm, plus vp8/9 and vorbis/opus being open codecs (even if vp8/9 was developed by a company google acquired, and vorbis is kinda old now). i hope av1 ends up making it as standard in webm since it's completely open (no google offering it openly but also holding patents on some parts nonsense).
i do wish they'd pick a different file extension (i'm a bikeshedder, alright ? )