I really don't think you have watched a lot of tape, I also think you have downplayed escapeability. Jacoby does have decent mobility although not what lucks was. There are times when a pass rush is going to beat an O-line. Even the greatest offensive linemen get beat, and then when you get blitzed heavily there are only so many blockers available and you need someone who can escape pressure when it comes. We aren't banging on the table for a Lamar Jackson or Mike Vick type but there is value to keeping a play alive when pressure is coming. How many games did Luck win us by being able to run outside the pocket buying enough time for a WR to get open and score a TD. Heck Manning utilized it during his roll out passes that where pretty dang successful. Mahomes is not a scramble first QB and his yards and TD's obviously prove that, but when you can use your feet as a weapon and add another dimension to your game it makes it that much harder to stop you. But how about you give Mahomes more credit? Led the league in passing in his first season as a starter taking them to the AFC championship game and now he's taking them to the super bowl. There is a very strong possibility we are currently watching one of the greatest QB's of this coming decade evolve.
the ravens have a good line and it made a difference for lamar jackson. they have an 8 time pro bowl guard
Lamar isnt exactly a typical scrambling qb either though. not many qbs run off the guard and up the middle but he does. a good RT is probably more important for most scramblers