I think you're on to something about consistent apple types. The type of apple that was standard in pies when I was growing up in the UK (and used in Branston pickle and probably a lot of other things) isn't even grown in the UK. They're inedible raw: a large, very firm apple that I remember with only a flush of red on the green. See Bramley apple (although this time I see some nurseries offering them in the US, so maybe I have the wrong type) and more broadly cooking apple.

On the other hand, this British food writer hates Bramleys, and yes, you do have to add sweetener to pies made with them.