Apples to oranges? Equating injury to size is a bit fruity in itself. How many times did Elway have surgery on his bursa sacks? Playing in high school, he tore his ACL and had it removed - that's right, he played without a left ACL in college and a pro. JE missed a total of 9 games as a pro due to injury including a torn tendon in his throwing arm, microsurgery on his knee and surgery on his shoulder among other injuries, they happen in the NFL. ... in fact, during his career, Elway only had 2 stretches of 2 consecutive years where he started all 16 games (1985-86 and 1990-91). 
Truth is, very few NFL players avoid missing games due to injury and Siemian's career is still just in his 3rd year. There is no way to predict future time missed due to injury and cetainly not by body size. Oh, and Trevor's injury wasn't "this year", it happened in the 4th week of 2016 and Trevor went on to play 10 more game with the injury after missing just 1 start due to it. How's those apples?