He is not as small and frail as the Gracie's claim, but he still look pretty skinny and with a small frame to me.I don't know, he never looked nearly as frail as they hyped him up to be. In fact, I think he was a high-level swimmer or something like that, if I'm not mistaken. I'll say this, looking at Kimura, who was about 5'7 and 180-something, Helio did not look significantly smaller to me. I mean, he was definnitely taller. Of course he wasn't nearly as muscular as Kimura, but he wasn't that much smaller either IMO.
I mean he pretty much looks like me and I consider myself skinny and weak as fuck.
About the Gracie vs Kimura the fight, like I said the Gracie's undoubtedly exaggerate the size difference as much as they can for propaganda reason, but I don't think a low quality black and white video where they are both wearing a GI (which hide their physique) is very reliable to judge.
And even from such a video is still clear that Kimura had a much larger and well built skeleton frame, just look at this video from 1:00 to 1:20 when they are both frontally filmed from a short distance during their entrances and compare how much more well built Kimura looks.
To me it look pretty believable that Kimura may have an huge streght and power advantage (on top of being a much better grappler of course) despite being shorter.