Then anubis adopts it itself, increases the amount of work that needs to be done and the bar stays the same again for everyone? Seems like mostly a non-issue unless there is an arms race towards ever more optimized solvers which I don't believe is possible.
> Then anubis adopts it itself, increases the amount of work that needs to be done and the bar stays the same again for everyone?
No, the bar doesn't "stay the same" for everyone interacting with Anubis.
My otherwise-perfectly-usable 8-year-old phone, which can't be patched to run a native solver, becomes even more unusable on sites gates with proof-of-work challenges like Anubis.
This is the whole problem with PoW. It forces thousands or millions or billions of client devices to do increasing amounts of useless work which is relatively easy for cloud-based attackers to adapt to, but very difficult for hardware-constrained and software-ossified mobile clients to adapt to.
In other words, it asymmetrically punishes the clients that it's not intending to punish.