I guess what's important is noting the care and attention that the fish receive, like how you mentioned yours doing good with water changes and care.My heart isn't necessarily up to bringing the visibly sick ones home, although I realize some people do try to help them, to your point of trying to give them quality even if they aren't going to get quantity of life.
I have a brick 'n mortar pet store close to me, and they do a pretty decent job of water changes and taking care of all of their fish including the bettas. When I got back into fishkeeping about 5 years ago, I went there and looked for beauty in color and fins and tail. I had a 20 gallon split into half and my boys lived a good life. I was a little dismayed at how the one in particular had such large fins and tail that he was struggling a bit. The next two boys I brought home were crowntails and did much better Then I set up a slightly smaller tank and returned yet again to the brick 'n mortar, and selected a little girl. The next boy I got was a King, as I'd read they are a little healthier and sturdier regarding being able to handle the challenges of their early life.
I agree, I'd never put it into words like this but I think you're right. We just lost our cat who we'd had for 13 years, and although my partner was researching into purebreds - again because of a better track record regarding health, we ended up going to an animal shelter and bringing home a wonderful, sweet, funny boy who is at least 7 years old
I'm really impressed with a local store here in regards to the care they show for fish (and other, often mistreated small pets and birds) and the knowledge the show. I'm also impressed with the health and quality of their bettas, though they have some dumbos with huge fins that I worry about. But I'm also deeply interested in king/giant bettas, and that's not something a regular pet store would have.
All the cats I've ever had were strays that appeared, or kittens from people who couldn't keep them, or rescues. I'm sorry to hear that you lost yours, though I'm glad to hear that you have another companion. Cats are the best - they really are such emotional creatures.