I’m currently working at one of the world’s largest consumer banks, and for a company that really should care about the accuracy of such things, I see “EST’ frequently all summer long.

In my experience, Brits refer to their time as "GMT" whether or not DST is in effect.

True; I should have said "most people refer to their local timezone in that way". (The reason I didn't was because at the time, I was referring to those specific timezones, not because I was picking on Americans.)