Okay, we'll narrow it down to their first 21 starts each.
Tyrod: 62.6% CMP, 206.3 YPG, 7.57 YPA, 29 TD, 8 INT, 5.07% TD%, 1.40% INT%, 96.9 Passer Rating, 6.81 ANY/A
Siemian: 60.2% CMP, 241.4 YPG, 6.92 YPA, 27 TD, 20 INT, 3.68% TD%, 2.73% INT%, 81.9 Passer Rating, 5.53 ANY/A
When you factor in Rushing & Sacks Tyrod goes up to 232.3 YPG and 35 TDs (1.67/G) and Siemian goes down to 231.9 YPG and 28 TDs (1.33/G).
Literally the only stat Siemian has an advantage in is passing yards per game, and that is completely negated by sacks & rushing...