I agree, but in every play design you go through all the variables that exist. And that's definitely a variable. What if we just chipped him to throw him off his pattern? Different ways of throwing a TE off his designed route and definitely the timing of the route. You certainly don't assume a free and clear path. Never.
I don't know if it was poor design so much as poor execution. If Maze leads the TE, it's a touchdown. The ball was underthrown which allowed Reid to make a great play on the ball.