I don't know mate. Certainly Wales were one of the areas of the UK to benefit from EU funding but I don't think it's as much as you would think. I read somewhere it was abut £600m per year and mainly through agricultural policy ad regional development grants. Given that Wales, as an area, had I think the second to lowest GDP of the UK, I would imagine that it would have been getting heavily subsidised by Westminster too. By how much I don't know.
It's one of those. They probably may have been better off as part of the UK being in the EU rather than out, but not necessarily being part of the EU but outside of the UK, if that makes sense. NI is the same, except it could join forces with the rest of Ireland and rely on them to pick up the deficit.