I wouldn't say too much mass(they probably have his ideal weight worked out early on these days but I'd guess given his height too much weight would probably restrict his movement and agility) I've not seen him up close yet but he looks lean(not thin/skinny) and strong to me and given his height advantage seems to handle most forwards quite well from what I have seen, I didn't see him being brushed aside but maybe we do need to see more of him if Pep does intend to loan him out. I don't think that is the reason for it though personally, I think it's defensive prowess, positioning, experience and so on.