Hawkeye having a hearing aid makes sense. He's around explosions all the time, his character in the comics becomes partly deaf, and Jeremy Renner is actually hard of hearing. No issue there. I thought it was a perfectly fine character development choice. Further, it's also common that if the hero has some sort of handicap, disability, quirk, etc., the villain might also have a similar quirk. It's a bit cliche, but cliches exist for a reason. There are narrative elements that can be explored with the dynamic. Plus, there's nothing wrong with writing deaf characters, nor with wanting deaf actors to play them.

The problem is the dog. The whole point of representation in media, as you imply, is that you aren't supposed to notice, or rather that your attention isn't supposed to be drawn to the representation overtly. It's not supposed to be a big deal that there are characters with non-normative qualities. They're just supposed to be characters who happen to have those qualities, and I would love to have watched the show and not really noticed.

But here's the thing: They wouldn't cast a one-eyed dog just because he showed up really well in the audition. You may not have noticed/cared that the main characters and the dog were disabled, but there is a zero percent chance that the multitude of people involved in the decision didn't notice that they cast a disabled dog to be in the show about the disabled hero and the disabled villain. That was an intentional choice, and it was a bad one. It telegraphs to the audience that the creators knew exactly what they were doing, which largely invalidates the purpose of media representation.

And again, I can't stress this enough, the dog has one eye. The dog is a superhero mascot character who is not only figuratively a wink and nod to the audience about what they were doing, but also literally looks like he was winking at the camera. It was too much for me.