Why not? If the right eco answer is to eat more of a certain kind of meat instead of quitting meat,
First of all that’s not likely correct info. I can’t see the uncited chart you posted but it certainly sounds untrustworthy. I’ve seen several charts in documentaries and research papers and they generally show roughly the same pattern, comparable to this chart.
But let’s say someone managed to convincingly cherry-pick some corner-case legumes that are bizarre outliers to the overall pattern. Maybe there are some rare fruits that get shipped all over the world. It certainly does not make sense to divide, disempower, and diffuse the vegan movement in order to make exotic fruit/veg X the enemy of climate action in favor of preserving chicken factory-farming. Not a fan of Ronald Regan but there is a useful quote by him:
“if you’re explaining, you’re losing.”
IOW, you’ve added counter-productive complexity to the equation at the cost of neutering an otherwise strong movement -- or in the very least failed to exploit an important asset we need for climate action. This is not an environmental activist move. It’s the move of a falsely positioned meat-eating climate denier strategically posturing.
The wise move is to consider action timing more tactfully. That is, push the simple vegan narrative for all it’s worth to shrink the whole livestock industry (extra emphasis on beef is fine but beyond that complexity works against you). No meat would be entirely eliminated of course (extinction mitigation is part of the cause anyway), but when a certain amount of progress is made only then does it make sense to go on the attack on whatever veg can really be justified as a worthy new top offender. The optimum tactful sequence of attack is not the order that appears on whatever chart you found.
The somewhat simplified take is: “if you can’t beat ’em, join ’em, then beat ’em”. Vegans are united and it’s foolish to disrupt that at this stage.