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.
FWIW, the current de-facto standard is set by xterm. Here is a relevant excerpt of its source code:
! Disclaimer: there are no standard colors used in terminal emulation.
!
! The choice for color4 and color12 is a tradeoff between contrast, depending
! on whether they are used for text or backgrounds. Note that either color4 or
! color12 would be used for text, while only color4 would be used for a
! background. These are treated specially, since the luminosity of blue is
! only about half that of red/green, and is typically not accounted for in the
! RGB scheme.
!
! Blue text on a black background should be readable.
! Blue backgrounds should not be "too" bright.
!
! Originally color4/color12 were set to the names blue3/blue
!*VT100*color4: blue3
!*VT100*color12: blue
!
! They are from rgb.txt respectively:
! 0 0 205 blue3
! 0 0 255 blue
! However, blue3 is not readable on a black background.
!
! Another choice was from the Debian settings:
!*VT100*color4: DodgerBlue1
!*VT100*color12: SteelBlue1
!
! From rgb.txt:
! 30 144 255 DodgerBlue1
! 99 184 255 SteelBlue1
!
! Some users object to this choice because the background (color4) is brighter
! than they are accustomed. Others point out that the different weights for
! the red/green components make it appear to be not really blue. Finally, it
! provides poor contrast against color13 and color14.
!
! The current choice uses equal weights for red/green (effectively adding a
! gray to the result). It is brighter than the original choice, and provides
! more contrast between color12 and color13, color14 than SteelBlue1 did.
! Contrast of color4 against black is slightly improved over the original.
!
! Some refinement is certainly possible (you are welcome to try) -TD
Make that what you will :-).That’s true for 256 colour and various other escape codes too. But I wouldn’t say it’s true for 16 colour pallet.