Honestly, I've seen angel dragons get flattened into these boring morality mascots lately. They'll have this shiny, wise creature that exists just to give the hero a pep talk or a magic feather, which is such a waste of the concept. The interesting tension for me is when their 'goodness' is actually alien and uncomfortable. I'm thinking of 'The Priory of the Orange Tree' with the Nameless One—a dragon-god whose very existence is a catastrophe, but whose 'children' are treated with reverence by some cultures. That's more compelling than a simple symbol. Or even in indie romantasy, where you get a dragon shifter who is technically an angelic being but acts like a possessive, morally gray love interest. The symbolism breaks down into something messier and way more human, which is where the real story happens.
A lot of older high fantasy used them as pure, almost elemental forces of cosmic good battling a demonic counterpart. It felt very chessboard. Now, I notice authors playing with the burden of that symbolism. What if being the 'angel' dragon means making horrific sacrifices for a greater good mortals can't comprehend? That internal conflict between their supposed nature and the terrible actions required to uphold 'order' is where they stop being symbols and start being characters. The good vs. evil gets internalized, and the reader has to decide if the ends justify the means.