Of course his height is an issue.
There's no possible way that his height can't be a factor. I think it's obvious that it doesn't have to be a limiting factor if you have other skills to offset it.
If you have the ability to scramble and get outside the pocket so you can find your wr's, you can overcome it.
If you have the ability to read defenses well and diagnose coverages, you can navigate the pocket and adjust your drop to put yourself in position to get the ball out quickly
If you have a high release it doesn't help your visibility but can prevent batted balls and allow you to throw to spots over the line on shorter routes IF you're adept at seeing the field and have developed strong communication with your receivers to where they know where to be in a given situation.
Russ is famous for taking deep drops in part because it buys him time AND gives him a better read of the field.
And yes, on shorter drops, he had a tendency to scramble sometimes because the protection wasn't good and sometimes because he needed to get outside to see the field. His tendency to not get the ball out quickly made his bailing more necessary.
But whatever the reason, yes, absolutley. The fact that he's less mobile, and limited in other ways is severely impacting his play.