Good points, but I think you're overestimating Tim's length in the guard. The only person that has really struggled with that was Jeff Monson, and that's because he's pretty much 5 feet tall.
Randy is roughly the same height as Fedor, but he passed into Tim's half-guard with relative ease and punished him accordingly. Fedor has sat in the most dangerous MMA HW guard in the world 2.5 times and obliterated his opponent without being rendered ineffective.
I don't think Fedor will finish Tim by TKO, but Fedor does not lay and pray, he sits in a guard, stacks his opponent's legs, postures up, and drops bombs. Tim Sylvia struggled with Randy Couture's ground and pound
from half-guard, and he's going to be in even bigger trouble when Fedor gets to that position