I agree with what you said regarding the statement i said…
However i do coach several (college level) jumpers also and so far evidence seems supportive. However, great short approach jumps do not always mean great full approach jumps so we will see when the season arrives. But on the same note, short approach jump distance is virtually all about strength and power (not much speed involved) therefore i could argue that building up a heavy bulgarian split squat along with weighted jumps and single leg movements have greatly improved the power of me and my athletes.
From the other coaches who have a TON more experience than me they have basically tried it all and are avid uni lateral guys…
I think bi lateral movements are very important early on in development but once “enough” strength has developed specificity of movements become more important and therefore so do uni lateral movements for jumpers.
I also want to add that my best parallel squat is 420 lbs and my best bulgarian split squat to parallel is 260 lbs.