It's common for people who approach helping animals from a quantitative direction to need some concept of "moral weights" so they can prioritize. If you can avert one year of suffering for a chicken or ten for shrimp which should you choose? Now, moral weight is not the only consideration with questions like this, since typically the suffering involved will also be quite different, but it's still an important factor.

One of the more thorough investigations here is Rethink Priorities' moral weights series. It's really interesting work and I'd recommend reading it! Here's a selection from their bottom-line point estimates comparing animals to humans:

If you find these surprisingly low, you're not alone: that giving a year of happy life to twelve carp might be more valuable than giving one to a human is for most people a very unintuitive claim. The authors have a good post on this, Don't Balk at Animal-friendly Results, that discusses how the assumptions behind their project make this kind of result pretty likely and argues against putting much stock in our potentially quite biased initial intuitions.

What concerns me is that I suspect people rarely get deeply interested in the moral weight of animals unless they come in with an unusually high initial intuitive view. Someone who thinks humans matter far more than animals and wants to devote their career to making the world better is much more likely to choose a career focused on people, like reducing poverty or global catastrophic risk. Even if someone came into the field with, say, the median initial view on how to weigh humans vs animals I would expect working as a junior person in a community of people who value animals highly would exert a large influence in that direction regardless of what the underlying truth. If you somehow could convince a research group, not selected for caring a lot about animals, to pursue this question in isolation, I'd predict they'd end up with far less animal-friendly results.

When using the moral weights of animals to decide between various animal-focused interventions this is not a major concern: the donors, charity evaluators, and moral weights researchers are coming from a similar perspective. Where I see a larger problem, however, is with broader cause prioritization, such as Net Global Welfare May Be Negative and Declining. The post weighs the increasing welfare of humanity over time against the increasing suffering of livestock, and concludes that things are likely bad and getting worse. If you ran the same analysis with different inputs, such as what I'd expect you'd get from my hypothetical research group above, however, you'd instead conclude the opposite: global welfare is likely positive and increasing.

For example, if that sort of process ended up with moral weights that were 3x lower for animals relative to humans we would see approximately flat global welfare, while if they were 10x lower we'd see increasing global welfare:

See sheet to try your own numbers; original chart digitized with via graphreader.com.

Note that both 3x and 10x are quite small compared to the uncertainty involved in coming up with these numbers: in different post the Rethink authors give 3x (and maybe as high as 10x) just for the likely impact of using objective list theory instead of hedonism, which is only one of many choices involved in estimating moral weights.

I think the overall project of figuring out how to compare humans and animals is a really important one with serious implications for what people should work on, but I'm skeptical of, and put very little weight on, the conclusions so far.