cats are known to cause devastation to all local wildlife

I'm pretty sure the RSPCB disproved this years ago, at least for birds, but I can't find that study.

they also spread diseases in gardens

So can foxes, badgers, rats etc. Most cats are vaccinated annually against diseases and will go to the vet for checkups regularly, therefore the risk is much lower.

they live shorter unhealthier lives

Shorter? Sure, but not because of disease. Traffic is a much bigger problem, letting cats outside in cities or near busy roads is a far greater risk to their lifespan and I would never recommend someone to do that. Claiming they live unhealthier lives is wrong too. An outdoor cat can get so much more exercise than an indoor cat ever could, reducing obesity (as long as it's not grifting for food with every other household nearby, which is rare).

It’s quite frankly inhumane to let cats free

It is much more humane in the UK (which is where I am and where the petition is) to let cats outside, and let them enjoy fresh air every day, discover new smells, socialise with other animals, and generally be so much happier, than trapping them inside from when they're a kitten until they either die miserable, or escape and find an owner who will take care of them properly.

it’s wild that there’s a place that won’t hold their owners accountable for the property damage they inevitably cause.

Have you ever met a cat? It is extremely hard to control what they do, and the law recognises that. Theoretically, a judge could rule that cats are under the same category as dogs, but a cat would first have to do as much damage as a dog could do. Only one legal case got close. where the cat "got into Mrs. W. ‘s, fiat ate mincepies and fish, got on to a bed, and scratched the bedpost". The judge sided with the cat owner.

Most places have updated their laws as new informations come out in the last 50 years

The UK has too, see the Animal Welfare Act 2006.

Those laws aren’t even based on scientific studies I believe. It’s all “feel good”.

The RSPCA and other organisations like them conduct studies and campaign for the law to be updated accordingly. The UK is one of the top countries for animal welfare as per World Animal Protection, and is significantly better than the USA.