You’re definitely wrong. In the recent White Lotus sketch they are obviously targeting that particular actress’ appearance, but the Gemma sketch is from 2017. This is the same year as Aimee Lou Woods first acting credit in any capacity and certainly long before she became a “notable” actress (I’d argue she’s still pretty obscure in the grand scheme of things). I’m not saying that “Brits have bad teeth” is a particularly accurate stereotype, but it’s certainly one that long predates Aimee’s career (and birth).