You're not wrong, but you can reference the whole thread about WR roles currently on the front page. Some people in there explain I better than me.
Samuel's on the shorter side, but not skinny/small. He has good hands can run any route Davis did. Davis is not a super-athletic, jump ball-catching boundary WR, anyway.
Samuel can get the production Davis did, while hopefully the star rookie takes over the WR1 role by year two, if not year 1. I'm hoping the replacement for Diggs has that contested catch ability and super speed in his arsenal.