I think the shape of the Kaboom has evolved ever since the other 2 'big' bats were launched. 50 plus is big edges and not a really pronounced spine, xp80 is all spine and small edges. Kaboom has relatively smaller edges but a slightly higher peak compared to the 50+.
I have seen David Warner's actual Kaboom in flesh that he gifted to Pakistan's Sohail Khan. Edges were smaller than my 50+ but had a very pronounced peak.
Your right. Not really such thing as a "true" kaboom considering its based on a profile thats always changing. Especially so when marketed as a replica. Warner has used so many different profiles in all formats of the game and as you say it has evolved. All you have to do is search google images and you can see countless different profiles. Just look at this as an example, might just be an xp80... but you get the picture.
Re Legend bats. I rate em but then i havnt owned a mid or lower grade GN so cant compare.