@GlomOfNit you paint a depressing picture of Oxford city centre. I just wanted to point out that the Covered Market is flourishing at the moment though! It's having a kind of renaissance I think. Loads of interesting independent food stalls and shops.
In general high streets across the UK are declining, due to online shopping and other factors; it's not just Oxford.
I agree that Cornmarket and Westgate are rather soulless, but at least they get plenty of footfall. I tend to avoid going into the centre on weekends because there are so many tourists this time of year that it makes me feel claustrophobic.
About cycling, no, it's not for everyone, but for those of us who do rely on it as our main mode of transport, it can be fine. You said, And I don't want to cycle in the heavy rain, or blustery winds, or the dark, or icy cold. And I don't want to cycle on my own as a woman when it's dark. And the bus drivers are a nightmare with cyclists. None of those things are dealbreakers for me. Heavy rain and icy cold are relatively rare, and I have good waterproof kit. In rainy weather, I frequently arrive at work and see people peeling off their waterproof trousers; it's not a big deal. Darkness is fine too as long as I have lights and high viz and know the route. I feel much safer cycling after nightfall than I do walking. And the bus drivers in Oxford aren't perfect, but they are extremely accustomed to sharing the roads with cyclists.
I'm not saying everyone can or should cycle, but fewer cars on the streets will make it easier for people who need to travel in cars/buses to do so, like your DS.