That isn't true. It absolutely matters which one is easier. because you have a sequence of events that has to take place. You are right that all of the things need to happen regardless, but how they happen matters.
Scenario 1:
100% XP (Recinos is 100% in his career)
18% Onside kick (based on statistics I found online)
25% Iowa has to score a TD again (Lets be real, wasn't happening so this is all just for fun)
41% 2 pt.
Scenario 2
41% 2 point
18% onside kick
25% TD
100% XP.
When looked at as a whole, sure they all equal out, but in order to get to the next thing in the sequence, you have to get through the first one. Give me the 18% of having the ball and a shot to tie with 1 minute left over the 7% chance of having the shot to tie any day. Especially when there is a 59% chance the game is over after the first step in the sequence.
You can go for two in that scenario if you have enough gametime to alter your play to try to get 2 more possessions. Iowa didn't have time for that so they were relying on one onside kick. That has the lowest probability of success of everything so why put yourself in a position where you would need 2 in order to be in the game.
You can argue this till you are blue in the face. Ferentz didn't have any idea what he was doing. Don't give me the BS that he was trying for the best chance to win. He was looking at his generic card that said when down 9 go for 2. He wasn't factoring in the timing at all.