100% this. After my first month of raising chickens, I quickly began amassing chicken first aid products. There are 2 boxes in my pantry full of treatments for various things. I bought corid the first year and never had to use it, I used it this year as a precaution when one chick fell ill, but ended up needing to bring her to the emergency vet for immediate treatment anyway. The only things I've had trouble sourcing has been antibiotics. There is very little you can treat chickens with (legally) because they are considered livestock/food and not pets.

We also had trouble finding vets- we did end up finding 1 very good one, and one that was more avian than poultry and was looking stuff up on the internet honestly not quite as well as I could have. But the emergency vet here has been fantastic- they've saved 2 of my chicken's lives. They have an exotics and livestock specialty unit (which is pretty much always an on call emergency - which means even more expensive than normal) but we are those kinda chicken owners, I guess.
When you'll go to pretty great lengths to ensure your pet's health and safety and then someone tells you to "cull" it- it never sits will. I know some people treat chickens like livestock, but to me, the "backyard" implies hobbyist or pet keeper. And I dunno, I wish people would remember that when they give that sorta advice. "Cull" seems to imply "this chicken is more trouble than its worth" whereas "euthanize" means quality of life is no longer good enough to justify trying to keep your pet alive. Two different connotations, imo.