I live in a relatively anglicised part of South Wales. I'm a first language Welsh speaker (my family are Welsh speakers). In person I hear "I wish I could speak Welsh" frequently. On social media I read "what's the point? It's useless outside of Wales. Everybody speaks English anyway" etc. frequently. I did French and German in comprehensive, German at GCSE. Do you know how often I've used either of those MFLs? I could probably count on my fingers. And when I have had the chance it's been on two weeks maximum family holidays (I've also learnt the polite basics in other languages for holidays too).
The cognitive benefits of acquiring another language far outweigh the negatives (of only being able to speak said language in one geographic area). I don't think all UK children should have to do a GCSE in a native language, but I do think an awareness of the basics (greetings, thanks etc.) needs to be brought to their attention. I also think the Westminster government need to promote the diversity of Britishness. I feel that Britishness is Englishness because it doesn't recognise or promote Cymraeg, Gaelic, Cornish etc. languages and cultures.
I have often heard that us Welsh speakers are insular and need to broaden our horizons. But in my experience, it's the other way round in Wales.