On the NHS, I tried for years to push for improvements to switch to digital cancer screening invitations after they missed my mother (offering to build the software for free), which is now happening, but suggesting the NHS isn't perfect is against the religion here. My sister who works in NHS DEI hasn't spoken to me since publishing a book on it.
Every time someone with the finances, vision and ability leaves I think the situation gets a little bit worse, it increases the proportion of people remaining willing to put up with all of it. Anecdotally, many of my friends have already left, some of the older generation want to leave but feel tied in. My flight out is in 6 weeks. Good riddance, no doubt.
That's really not my experience. In fact, almost everyone is surprised when I suggest that despite its many problems, the NHS does better for the people than most modern countries' health systems.
No one I know who has lived in France or Germany or any developed country other than the US thinks the NHS is better than the systems in those countries.
There are times I opt for private services for speed, because I can afford to, but I could also afford private health insurance (which is cheap in the UK), and haven't felt the need to.
That said, dental is a weak spot of the NHS, with too few dentists offering NHS services, and there's a perceived quality difference in that the NHS treatments have fee caps that mean they will often not include the best aesthetic options. For dental I do tend to go private (but dental for adults is also excluded in quite a few other "universal" healthcare systems - like Norway; don't know about Spain)