Wales is more akin to Northern Ireland than to Scotland, in that there is a huge divide between populations, in this case between monolingual south-eastern and north-eastern places and bilingual western parts. That was reflected in the Brexit vote - people who can speak both languages were strongly anti-Brexit, and the people in the English speaking areas who had to walk past signs saying "built with EU money" on the side of the polling station voted leave.
Plaid Cymru is much stronger in areas where English is less dominant.
Welsh independence is hindered by this, and also by how small Wales is. It is tiny, approximately only the size of Wales.