I took Latin O level, loved it, liked my teacher, but we studied the Cambridge course and it did not really cover much in the way of grammar, and I cannot read or understand Latin at all now (except Caecilius est in horto obvs). I have never needed it in any of my work - not even when I worked at a famous museum of ancient history and archaeology!
Was it a waste of time? For me, not at all. I could have done geography or biology instead, but I didn’t like either of those subjects as much, they wouldn’t have made any difference to my choice of degree (Economics), and I almost certainly wouldn’t have used them in my future career any more than I used Latin.
To answer the OP, No, I don’t think so. I agree with PPs that learning Latin in order to help with the grammar in another language is nonsense - they should teach the grammar of all languages as they are being learnt. What improves educational outcomes is teaching a range of subjects and teaching them well, hopefully firing pupils with the enthusiasm for learning all manner of things, which are not necessarily purely utilitarian, just for the sheer hell of it.
DS has his last Latin GCSE exam tomorrow. He has been taught it brilliantly, and has the most incredible knowledge of both the grammar and vocabulary. He loves the subject and is going to do it at A level - along with Greek and two MFLs. Languages and linguistics are his ‘thing’, the way some people are maths people or science people, and Latin has been useful to him in this.
PPs have expressed a need for much better MFL teaching, for this we will need to continue training MFL teachers who will have a good understanding of the grammars of several languages and, most importantly, who love them.