I steam or roast. The only veg I boil are peas , older broad beans ( young fresh broad beans and indeed peas, are delicious raw) and sweet corn. But broadly I would say you are right, especially of the older generation.
The only thing I would disagree with is poached chicken ( or fish) . Done in stock with aromatics and gentle spices, it can be absolutely delicious.
It’s a very interesting question. The same complaint was made of British cooking in the 19th c !
More recently, olive oil for cooking was unheard of in this country until the 50s when people started to travel abroad again post war, and the 60s with the influence of Elizabeth David and the Roux brothers. It was largely used for medicinal purposes only before that. And butter of course was very expensive, and rationed well into the 50s. In contrast to say France, the population of England was and is, largely urban with the historical lack of access to good fresh food. Now of course anything is available from anywhere, which is both good and bad.
Generalising wildly I would say the traditional British palate was somewhat unadventurous with a preference for the bland. Possibly influenced, as someone pointed out by the very basic and often shared and limited cooking facilities in urban slums. This is of course changing radically with immigration and globalisation, worldwide travel bringing influences from all corners of the globe, and the popularity of food programmes on TV.
I vividly remember my first taste of good French food in Brittany aged about six, in the early 70s. An absolute revelation for all the senses. I have been a food lover and Francophile ever since.