Ted Hendricks was 6'7" and never weighed much over 235 until late in his career, and never played at 250. It didn't have any relationship to how strong he was. I recall a play in San Diego on a Monday night when Ted stayed home against a misdirection and faced Chuck Muncie (6'2" 225) with a full head of steam coming off the edge: Hendricks stopped him with a forearm to the shoulders and in the next motion threw him down.
There is a reason the award for the best linebacker in college football is named after him.
Key is bigger now than when he put up those insane numbers the year before he came out. Functional strength is a combination of physical strength, leverage and will. He doesn't have to get all three aligned to the level of Hendricks in today's NFL, he just has to learn all the subtle tools about hand fighting, deception and leverage, and get all he can from film and translate it to games.