But you can argue that for almost every other European country inc other parts of the (for now) United Kingdom and yet they do have stronger defined identities today. Right now. Currently. England is very diverse and tribal which makes it hard to define in any unified sense. Maybe that's our definition. The square peg that won't fit into any round holes! I'm sure there are better definitions mind!
Oh I think we would be able to define Englishness if we tried. I'm also sure that many Germans, French, Spanish and Italians would say that there identities are being eroded as well. They are not. They may be changing, but then again all identities change as time and events shape them.
Like you, I like celebrating my Englishness, just as I'm fully supportive of the Irish, Scots, French, Welsh etc etc celebrating theirs. It's important. I think Notting Hill Carnival for example is a very English thing - celebrating a culture that has been brought to our capital city and has enriched it over time. I think Pride is very English - that gradual acceptance over many years that men and women should be able to live their lives the way they want as long as they are not harming anyone else.
We could write lists of what's 'English' and be very proud. Equally, so could other nations.
Our identities are carved into us by events. Some peaceful and slow burning; some sudden and violent. Shane Duffy grew up in a community where that violence was all too prevalent. McGuinness may well have been a terrorist, and that will always be unforgivable, but he fought for his community and then he changed. Mandela famously support the reconciliation of those that had persecuted him so that South Africa might stand a chance. We all need to take that character forward in my humble view.