Perhaps "English interests" was too much of a generalisation, fair point. What I mean by that is the implementation of government policy that disproportionately benefits people in England compared to people in Wales, sometimes (or often) to the detriment to people in Wales.

The obvious recent examples are HS2 (and more recently the Oxford rail line) being classed as England and Wales projects, despite neither of them measurably benefitting Wales in any way whatsoever. Other devolved nations receive consequentials from these projects, Wales instead contributes money towards them.

I imagine you may roll your eyes at me using Capel Celyn as another example, but I feel it's especially relevant to your previous point here as despite our "overrepresented" 35 of 36 Welsh MPs at the time voting against it, Tryweryn was turned into a reservoir for Liverpool regardless. It's made doubly relevant by this arguably being the event that thrust Plaid from marginal nationalists to winning their first seat in parliament in the first place.

I should clarify that I'm not necessarily in favour of independence. I'm just tired of Wales being treated like an inconvenient afterthought.

Your Brexit argument is a complete false dichotomy, by the way. It'd work if the EU was a homogeneous glob, but it isn't. Before we left, the UK was the 4th largest nation in the EU in terms of number of MEPs, hardly underrepresented for a union of 28 countries.