I get that there are some comments about the similarities between humans and angels during instrumentality, but how are they enough to conclude that they are humanity's competitors in evolutionary race? Angels don't eat, don't sleep and don't seem to be able to procreate. On top of that, two of them show and ability to sacrifice their life, something that no creature wishing to procreate would opt for. Given how their bodies suffer from crippling overspecialization, wouldn't it be more adequate to see them as living weapons, something they are already described as in early materials on the show's concept? Gendo describes Sachiel as "autonomous weapon" in the very first episode, so why is there such confusion on the matter?

I think a lot of this comes from some of the lore that's only given in supplementary material like games and the like.The angels are children of Adam just like Humans and all other lifeforms on earth are children of Lilith. While each angel may be itself a unique species, they all come from the same root. So by virtue of being of Adam, it means they're competitors to Humans. Whether they're also competitors to one another doesn't really seem to matter, as they all have essentially the same goal - which is to start the Third Impact and take Earth back from the Lilin. Hypothetically, if they were to do this, life would be either destroyed or remade in a way which would allow those from the seed of Adam to procreate or do whatever it is they would do. Considering how they seem to be able to bypass AT Fields and do mini-instrumentalities against Shinji, Asuka, and Rei it wouldn't surprise me if they have little desire to procreate and instead would assimilate other life or something. But that part is coming totally from my head, so don't give that theory very much credence. Either way, even if the Angels aren't one solid species, they're the same sort of category or they're in the same domain.