English teacher conspiracy

It looks like English teachers have some kind of a conspiracy to lead their students astray.

I remember clearly a lesson where half of the class had to be taught to pronounce "data" as /ˈdeɪtə/ (first "a" like in "fate"). Everyone learned well, thanks to the famous lieutenant... and now it turns out about half of the native speakers naturally say /ˈdɑːtə/ (first "a" like in "cut").

And yesterday I learned the capital of the United Kingdom doesn't have to be /ˈlʌn.dən/ (first "o" like in "some") - saying just like everyone read it the first time in a textbook - /ˈlɔn.dən/ (both "o" sound the same) is also okay.