Not well completed, but I will post this anyway,
for what little it is worth.

Why are some Welsh very disgruntled with the English,
while others are only mildly so, and others just fine
with them?

Hmm, I suppose old time grudges and prejudices.
And, to some extent, I guess this is similar to why
citizens in the USA in more rural states express
discontent with the coastal elites.

Some talk and jokes and stories are good fun,
others go to grow into hate.

I read in:
https://en.wikipedia.org/wiki/Wales

Llywelyn ap Gruffudd's death in 1282 marked the completion of
Edward I of England's conquest of Wales, though Owain Glyndŵr
briefly restored independence to Wales in the early 15th century.
The whole of Wales was annexed by England and incorporated within
the English legal system under the Laws in Wales Acts 1535 and 1542.

interesting enough read
https://cherwell.org/2020/07/19/cofiwch-dryweryn-a-welsh-history-of-oppression/

overstated, but still:
why do the welsh hate the english
About 32,600,000 results (0.73 seconds)
Other factors include sporting rivalry, particularly over rugby;
religious differences concerning nonconformism and English episcopacy;
industrial disputes which usually involved English capital and Welsh
labour; resentment over the conquest and subjection of Wales; and the
exploitation of Wales' natural resources such ...

Here is quite a volume to read:

Why does Wales hate England and vice versa? - Quora
https://www.quora.com › Why-does-Wales-hate-Englan...
Jun 28, 2016 — The Welsh hate the English (rightly so), because for
centuries the English tormented and abused Welsh people, making them 2nd
class citizens in their own ...
7 answers
4 votes:
There are some justifiable reasons for the Welsh to dislike the English
:- 1) they flooded ...
Do the Welsh and Scottish dislike the English? - Quora
21 answers
Aug 3, 2017
What do the Welsh think of English people that live ...
36 answers
Sep 15, 2015
What do English people think of Welsh people? - Quora
10 answers
Feb 27, 2019
What do the Welsh think of the English? - Quora
6 answers
Dec 20, 2018
More results from www.quora.com

On Tuesday, November 9, 2021 at 11:32:28 PM UTC, a425couple wrote:
> Not well completed, but I will post this anyway,
> for what little it is worth.
>
> Why are some Welsh very disgruntled with the English,
> while others are only mildly so, and others just fine
> with them?
>
> Hmm, I suppose old time grudges and prejudices.
> And, to some extent, I guess this is similar to why
> citizens in the USA in more rural states express
> discontent with the coastal elites.
>
> Some talk and jokes and stories are good fun,
> others go to grow into hate.
>
>
> I read in:
> https://en.wikipedia.org/wiki/Wales
>
> Llywelyn ap Gruffudd's death in 1282 marked the completion of
> Edward I of England's conquest of Wales, though Owain Glyndŵr
> briefly restored independence to Wales in the early 15th century.
> The whole of Wales was annexed by England and incorporated within
> the English legal system under the Laws in Wales Acts 1535 and 1542.
>
> interesting enough read
> https://cherwell.org/2020/07/19/cofiwch-dryweryn-a-welsh-history-of-oppression/
>
> overstated, but still:
> why do the welsh hate the english
> About 32,600,000 results (0.73 seconds)
> Other factors include sporting rivalry, particularly over rugby;
> religious differences concerning nonconformism and English episcopacy;
> industrial disputes which usually involved English capital and Welsh
> labour; resentment over the conquest and subjection of Wales; and the
> exploitation of Wales' natural resources such ...
>
> Here is quite a volume to read:
>
> Why does Wales hate England and vice versa? - Quora
> https://www.quora.com › Why-does-Wales-hate-Englan...
> Jun 28, 2016 — The Welsh hate the English (rightly so), because for
> centuries the English tormented and abused Welsh people, making them 2nd
> class citizens in their own ...
> 7 answers
> 4 votes:
> There are some justifiable reasons for the Welsh to dislike the English
> :- 1) they flooded ...
> Do the Welsh and Scottish dislike the English? - Quora
> 21 answers
> Aug 3, 2017
> What do the Welsh think of English people that live ...
> 36 answers
> Sep 15, 2015
> What do English people think of Welsh people? - Quora
> 10 answers
> Feb 27, 2019
> What do the Welsh think of the English? - Quora
> 6 answers
> Dec 20, 2018
> More results from www.quora.com

Many are reasonably gruntled with the English.
There is little support for independence, for instance.
But, like the Scots, the Welsh are very different politically to the 'ruling' English Parliament.
Now having a Welsh Parliament helps to some extent here.
And the "Welsh" Welsh (as opposed to the many English and others living within Wales) ARE also very different sociologically and culturally - many as regards language especially, for instance.
And there are many English intrusions such as English-owned second homes, causing housing problems for the locals.
Etc., etc.
But most Welsh live alongside reasonably happily.
Except for when there's a Wales/England rugger match on.