ΔE 23.9, loose: different enough that you should pick on purpose. Legacy Blue is a little darker, much more muted, cooler than Leviathan Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Legacy Blue is a little darker, much more muted, cooler than Leviathan Purple.
The same difference applies the other way round: Leviathan Purple is a little lighter, 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 Leviathan Purple on the colour wheel See Legacy Blue on the colour wheel
All matches: Leviathan Purple equivalents · Legacy Blue equivalents