From what I’ve learned over time, traditional bitter ales are usually about balance rather than extreme bitterness. They tend to have a noticeable malt flavor with moderate hop character and are often brewed to be smooth and drinkable. I remember looking into a small Cornish brewery that makes this style, and while reading about it I came across
this brewery site which explains some of their beers and the approach they take to brewing classic ales. A friend of mine visited Cornwall last year and tried a couple of their bitters in a local pub, and he said the flavor was more about subtle malt sweetness and gentle hops rather than the strong bitterness people sometimes expect from the name.