EJ's first (and second) season vs. Tyrod's first season as a Bill are completely different circumstances. EJ is playing out a rookie contract and there was no pressure to decide whether to try to extend him based on what can charitably be described as 'uneven' play. Tyrod on the other hand is a free agent at the end of next season and by any number of objective or subjective measures is on a trajectory to establish himself as an above average starting quarterback. It's only 10 game sample in regular season but he's 6-4 on a team with an average defense, a QBR rating in the top 5 in the NFL, and impressive running statistics and capabilities. Each game we get more data by which to update our estimates of his longer term value.
Here's the conundrum however: the more quality starts Tyrod produces over time, the more he's valued as the uncertainty about his capability level goes down, the more the Bills want to keep him long term, the more they have to pay as they wait longer to sign him to an extension. However if Tyrod starts to put together poor games, the lower his perceived value goes, and the less the Bills are even interested in resigning him anyway. Of course we could end up somewhere in-between with mixed results.
Where I end up on this is if the next four games go about as well for Tyrod as the prior ten, it behooves the Bills to sign him to an extension in the off-season. Training camp, pre-season, and fourteen regular season games played for a guy who got to be an understudy in Baltimore for 4 years should be enough to know that at worst they'd be getting an average QB who gives them a chance to win if the defense is solid at all. They could get him at reasonable market rates this off-season. I question whether the incremental data gained by another full regular season of games is worth it in terms of understanding his downside risk compared with the possibility that his price tag goes up much higher and they possibly lose him to another team with more cap space.
Again, not saying to extend him right now, or even in the off-season if he seriously falters in the next four weeks, but if he continues playing like he is I say lock him up for another 3-4 years at least this upcoming off-season.