> does it actually raise the cost or reduce asymmetry in a meaningful way?

It's complicated. I think anubis currently only collects low hanging fruit so to speak but in practice that's the bulk of what was causing problems so it's good enough.

PoW in general absolutely yes - I think monero clearly demonstrates this. Last I checked it remained viable to mine monero on at least somewhat low end and at least somewhat outdated consumer CPUs. It seems to me that fact implies that a well constructed PoW scheme can in practice squash the impact of any performance differences to within at most a couple orders of magnitude.