Not saying I agree, but Deep is saying it would be foolish to pick up a player Harbaugh doesn't want because he doesn't fit his scheme. Forget about Snyder, he isn't focusing upon that. That sounds like a distracter on your part. And I believe you already knew that but this was an easier point to make (that Manning > Snyder) There's a good argument for why it isn't foolish to pick Peyton up, you shouldn't jump at a false argument.
I think it's an easier point to make that it's ridiculous to say Manning doesn't fit a system.
What does our system involve that Manning would not be able to do? If it's the running QB part, Smith only ran 52 times this year (barely over 3 times per game). How may of those were designed runs? I'm pretty sure Manning would be able to find a receiver on a lot of the Smith scrambles.
However, what more can Manning bring to the system that Smith couldn't? A lot of passing routes will open up that Smith either wouldn't throw, or couldn't throw if we were to add Peyton to the roster.