Why does the length of time matter? Domesticated varieties of cows and pigs would go extinct if humans stopped raising them for meat. The only niche where they can survive is a farm. They are in symbiosis now even if they weren’t 10,000 years ago.
Time matters because that’s how evolution cements biological distinction. Domesticated cow and pig varieties can certainly survive off of farms. There’s the famous example of the cow that escaped to live with a herd of bison, and feral pigs are a well known phenomenon. Yes they are in symbiosis, but it’s not biologically obligatory symbiosis.
By that reasoning, fruit is not in a biologically obligatory symbiosis with the animals that eat it. There are many cases of fruit falling to the ground uneaten and forming a new plant near its parent. Those plants eke out an existence just as feral pigs do.
Yes, and this is an undesirable result. You can eke out an existence with no legs, but it is not the preferred state of things. You’re just debatelording now.