He was originally a 2* recruit and like 3,200 ranked player in the nation. His only offer was from Houston. RS his first year in 2015, played in 8 games his second year but totaled only 61 snaps, third year played in 3 games, started two, fourth year started 13 games at RT, fifth year played in 4 games then had a season ending injury, sought a medical RS.
Overall he had one good season 2 years ago and is coming off an injury. Don't get me wrong I agree he is better than his ranking and want him as a player, but I can see the reasoning for having him in the high 3-star range. Also I think he is top 5 for transfer tackles in terms of rankings. Walker is high up there because he is essentially maintained his HS recruit ranking, Cade Mays the former 5 star from UGA was up there, then some randoms and Williams.