However, birds mercilessly teased him as he had no clue how to catch one, surrounding him while he lay on the grass, chirping, then flying just far enough away when he'd move towards them.
There is no real genetic difference, as a total population, between feral cats and cats owned as pets. Absolutely, as you point out, owned cats who know they'll get fed inside will murder outdoor animals just for fun, and they don't need to eat them to survive - but that's a learned behavior, nothing they were bred for. You take a normal tabby and leave it to have its litter outside, unowned, and those cats will turn into feral cats.
Many animal rescue organizations have developed "Barn cat programs" for feral cats. These cats have not been socialized to be around humans so they make bad pets, but they're happy to live in a barn and ensure it says rat-free: https://www.austinpetsalive.org/programs/barn-cat-program.
> We estimate that free-ranging domestic cats kill 1.4-3.7 billion birds and 6.9-20.7 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality.
From the text of the paper, "majority" means 69% for birds and 89% for mammals. Feral cats kill a lot of animals, because that's what they eat. Pet cats do not. "Domestic cat" here means F. catus, not cats that live in homes.
Also, i wouldn't attach complete confidence to this paper. Firstly, it was written by bird conservationists, who have a dog in this fight (as it were). Secondly, it contains some dubious numbers (eg bird return rate per owned cat per year of 4.2 - 18.3 in US and Europe studies - and yet my mum's cats all brought in 0 - 1 per year). I'm not saying ignore it, but don't treat it as gospel - and it would be great to see responses to it, and other work on this subject.