When I lived in Swansea, there were no Welsh lessons in school and I don't recall ever hearing Welsh spoken in the south but a couple of months before my 11th birthday, my family upped sticks and moved to Llandudno on the N Wales coast and on my first day at my new primary school, I was being taught Welsh and this continued during my 1st year in grammar school until I was able to drop it but I never caught up as I was too many years behind my classmates. I would say there were about 25-30% of my year who were fluent in Welsh and I would hear it used regularly outside of school and almost exclusively in more rural areas so it was definitely far more widely spoken than in the south. This was in the early 60s so I would imagine the proportion of fluent Welsh speakers will have dropped considerably by now but in my experience, the North was definitely far more 'Welsh' than the south. Not sure how Welsh Wrexham would have been though, being so close the English border.