ΔE 31.7, loose: different enough that you should pick on purpose. Radiant Platinum is noticeably lighter, much more muted, cooler than Runelord Brass.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Radiant Platinum is noticeably lighter, much more muted, cooler than Runelord Brass.
The same difference applies the other way round: Runelord Brass is noticeably darker, much more saturated, warmer.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Runelord Brass on the colour wheel See Radiant Platinum on the colour wheel
All matches: Runelord Brass equivalents · Radiant Platinum equivalents