(b) is relevant if you think that the qualia of consciousness has a bearing on the ethics of eating meat.

>Unless the word “equivalent” is playing a critical role for you, because it will be impossible to prove or disprove equivalence.

To be clear: I haven't actually stated my position in this debate.

More to your point: this entire debate is an ethical one, so it's in the philosophical realm, so one should disabuse oneself of the notion that anything is going to be "disproven". The best we can aim for is a consistent ethical system, and conversely, the pointing out of inconsistencies.

This having been said, there's a contradiction of terms if you simultaneously hold the belief -- as you seem to do -- that eating animals is wrong because they are in some sense "like us" while at the same time rejecting any notion of (non)equivalence. You exactly appeal to equivalence when you say, "Really, other animals are so similar to us on every dimension except language". So you are being inconsistent.

Therefore, if this is indeed your position, you're going to have to grapple with the issue of threshold. How much similarity is too much? Holistically, is the experience of being $ANIMAL equivalent to (or within some bounds of) the experience of being human? If there are differences, which ones matter and which ones don't ... and in what amount? Those are the questions the GP was asking, and they are directly relevant to the argument.