imagine my delight when in the middle of weeding between my cabbages I noticed a beautiful white perfectly formed cauliflower head peeping out between the leaves
now that you've weeded, just make sure the pigeons haven't eyeballed it so go cover with netting asap!!!!
I like nice surprises like this - just when you think it is the worst year ever and out the blue something you didn't expect to survive let alone turn into a perfect crop appears. It doesn't happen often but when it does, you just know you can't throw the towel in just yet.
Caulis aren't really difficult to grow - they are just plain fussy. As you say, perhaps your soil is best suited (would it be heavy clay by chance? Caulis like their roots to be well firmed in) In which case you shouldn't really have problems with other brassicas such as cabbage and sprouts.
Let's have a look at the other things:
onions - if they were planted in spring, then they'll still be bulbless until later so don't despair yet.
beetroot - ages ago after sowing we have had some contrasting weather, from heatwaves, chills to deluges. Perhaps try a fresh sow instead of relying on the original one - the soil temperature should be considerably warmer so will germinate quicker and that's half the problem solved. They should then go with the momentum and grow more quickly - crops that falter mid way through their growing season tend to sulk afterwards. If you had done successional sowings of beetroot (a few seeds every other week), you might have noticed that later sowings tend to gallop and overtake earlier sowings
(that applies to lots of crops BTW)
If you've had lots of rain in your area, this may have washed some nutrients out of the soil. Digging in compost is well and good at the start of a season but when the weather is not helping either, perhaps look at fortifying the soil with a fertiliser for now to give your plants a bit of a boost is needed. Even a scattering of Growmore round the plants can be more helpful than none at all. In the long term, why not start thinking about making your own liquid feed (from weeds, manure or comfrey - you soak until they turn into a vile smelly brew then dilute down when watering crops) or start a worm compost.
Good luck with the plot Helen - and I hope you enjoyed that cauli (well done you)