depending on your use-case, you might get away without support for linked samples. Fluidsynth currenly doesn't consider them (and has never done so, I think). So in that regard it does not actually conform to the official spec. But as far as I know, we have never had a bug report about a Soundfont not being played correctly due to missing sample link support. It seems like there are very few (or none?) Soundfonts with different pitch generators for left/right samples out there. Or Soundfonts where the sample link is used for different purposes other than a left/right split.