If I was the maintainer of a terminal emulator, I would see a quite obvious way to improve the situation for my users: change the default colors so that dark blue is brighter.
There's no obvious way to unilaterally improve the situation across the whole ecosystem, that's true. But I don't understand why individual terminal emulator maintainers don't fix it for their users.
Quite a few terminal emulators do this already. Including the one I maintain.
Because it means making choices, breaking assumptions, etc.. They have made it user-customizable so they don't have to go through all that.
FWIW, the current de-facto standard is set by xterm. Here is a relevant excerpt of its source code:
Make that what you will :-).