i looked up the odds for a series ending in different games (assuming 50:50 win odds). the chances of a series ending in game 6 are .3125. divide by 2 since if the royals win in 6, no one cares if ventura didn't pitch. so you have a 15.625% chance of losing in game 6 with ventura not pitching.
so multiply .15625 x whatever % difference you think there is between cueto and ventura. i have little confidence in cueto, so i'll say .55 for ventura (home game) and .40 for cueto. .15 x .15625 = .02344. so is .02344 larger or smaller than the purported benefit of pitching cueto at home?
i don't know how to estimate that, but given that the negative impact of having ventura pitch game 7 is smaller than i would have guessed, it may be a tradeoff worth taking (i also looked up cueto's career splits, and he is worse on the road, but i don't know if he is more wore on the road than the mean that pitchers are worse on the road).