Billy is enormous compared to Sinckler. Height alone makes a big difference and Vunipola has a good 4 inches on Sinks. Beyond that, Vunipola is evidently larger built in every aspect other than the belly; just look at their lower bodies - Vunipola’s legs and butt make Sinks look almost civilian. While I don’t fully believe either of these figures, Vunipola is listed on the Sarries site as 130kg and Sinks on the Quins website as 115kg. Billy’s said that he prefers playing at the 132 mark and Sinks must be bigger than 115, but still, there’s a huge difference between the 2. Edit: Found this photo of the 2 next to eachother. Builds aren't massively dissimilar although Billy's legs are noticeably larger. The big difference is in the height. I'd have thought Billy has a good 10kg on him at least.