Your experiences of food in the UK don't match mine, and I've travelled plenty. In most places in the world you'll find some specialities done well, but I've yet to find anywhere with a greater range and depth of culinary options than London (although any truly global city will compete).
I rarely eat supermarket bread as we make our own daily. We mostly use Marriage's flour, which is available in many places, including Waitrose. That said, the bog standard Chorleywood stuff is comparable to equivalent products in Europe and decent farmhouse loaves, San Francisco style sourdough, baguettes, ciabatta, pain de campagne, etc. are all widely available in supermarkets. I can obtain more specialised baked goods from any of at least 4 good bakeries a short walk from my house.
As for cheese, France, Italy and Switzerland do have some wonderful ones, and I can obtain many of them any time I want from the cheesemonger down the road. As often as not, though, I'll buy something UK made. Baron Bigod is better than any Brie de Meaux I've tried and while Roquefort is briefly entertaining in a salty sort of way it can't compete with Colston Bassett Stilton. I don't recall seeing much of any of them in Mediterranean countries.
I can't speak for coffee as I don't drink the stuff. I'm pretty sure I could obtain just about any kind of coffee in the world with ease here, though, if I wanted to.
The tyranny of "healthy" food is the exclusion of experiences for no good reason. There's nothing wrong with sugar, fat or salt, you just need to avoid eating too much of them (or too little in the case of fat and salt). By far the most effective tool for that is good old-fashioned calorie counting, and thank god that alongside the various ill-judged public health measures in the UK there's also now the requirement for most food sellers to provide calorie info.
FWIW my dinner last night was homemade olive and garlic sourdough, which I had with some Ubriaco Rosso and some Godminster Cheddar. Delicious and life-affirming. 820kcal.
I don't know where your obsession with turnips has come from. I think I've only ever had them as part of Cornish pasties, which rule. I'm more of a swede man myself - give me haggis, neeps and tatties any time.
