Rather than the major chromatics being a species of dragons and collection of those that grow from egg to ancient wyrm, could D&D instead be a space where every dragon has different abilities, different temperaments and different looks?
They already are, as your example of Themberchaud shows.
The question I would have is what are you losing and gaining by such a change?
I don't honestly think you gain anything at all. While it's a really good thing if each DM pours creativity into each monster that they create and gives them personalities, temperaments, memorable appearance and different abilities, you already have that. If you don't utilize it, you can't blame the game for it.
What you lose by making everything wholly unique is any sense that the players might have that the world is predictable and sensible and knowable. For all your creativity you end up with Nitro Ferguson's "Kraag Wurld".
One thing that you should always avoid as a GM is the temptation to do something solely to impress, intimidate or terrify your players. A very little "Gotcha" goes a very long ways. Imagining how an encounter is going to play out for balance reasons is a good thing. Imagining the emotional reactions of your players to your creation is probably not a good thing.
Forcing yourself to make every single encounter that diverse and original is also probably not good for your sanity or prep time as a GM. Having a set of stat blocks to work from and inspire creativity or just grab because now you need a random encounter is a good thing.
When I set about making dragons have the lore that I wanted I created this thread:
AD&D 1E - Revised and rebalanced dragons for 1e AD&D
There is a massive amount of diversity just in that. Five chromatic dragons in three sizes of two sexes of ten age categories some with wings and some without, some lithe and sinuous, some talking, some with spells, some especially poisonous, some with multiple heads. There are like 500 or 600 combinations even before I get into sea dragons, turtle dragons, shadow dragons, and metallics, undead dragons and half-dragons and all the diverse drakes that inhabit my campaign world.
Dragons appear in all sorts in my campaign world, from hatchlings looking for new territory to settle, to young adult marauders, to ancient things with vast wastes and desolations around them where civilization is rolled back and none dare tread.
