(so, is the EU also saying that once a standard becomes big enough, every essential patent must be licenseable under terms the EU finds acceptable, even if the patent holder didn't agree to that beforehand or possibly even participate?)
It is not cross-licensing agreement per se being investigated, but
1. the inherent absence of some patents required for the standard/implementation to function in initial patent pool 2. use of pre-established market dominance of founding members to limit non-member patent holders' ability to create competing standard and effectively strong-arming them to join.
A very similar issue has been raised against Microsoft in the antitrust case regarding iexplore. Iexplore has been deemed "good enough" default that market dominance of Windows with iexplore preinstalled as the default effectively strong-armed everyone involved to at least maintain compatibility with iexplore.
I guess this is the disconnect; AOMedia worked very hard during standardization to avoid infringing existing patents held by non-members. There is a very strong belief that Sisvel’s claims on AV1 are fundamentally invalid, and while that would be nice to prove in court, Sisvel’s members arent stupid enough to directly sue anyone that can seriously fight back. Thus, the terms to license the actually essential patents to at least limit the damage Sisvel can do.
Anyway VVC is already technologically superior for anyone that wants a competing standard. If it fails, that’s 100% on the behavior of HEVC patent holders, not because of AOMedia.
Note that the EU isn't claiming that the standard itself is bad. They're saying the cross-licensing terms are anti-competitive. The cross-licensing may have made sense for major companies like Apple, Google and Meta but it significantly disadvantages smaller companies which may need to rely on their patent arsenal as a deterrent but also face economic pressure to adopt the standard.
This whole thing seems to be a breeding ground for submarine patents, where in the end nobody has an actual applicable patent to show but the thread of pulling one out of the hat is there to make things worse.
They have to join AOM if they want to use AV1 and they need to use AV1 if they want to be relevant because all the big players banded together and made that unavoidable. That’s the heart of the anticompetitive argument.
Most companies don’t exist to sue for patent infringement. They are not patent trolls. The point of competition law is that they should be able to do business without having to go to court with a conglomerate.