Yes, I would have much preferred to roll the dice with one of the other guys than starting a guy on 3 days rest when we know there's a track record of guys on 3 days rest pitching poorly. And again, those guys who typically go on 3 days rest are your ace types who are much better pitchers than Matthew Boyd. According to The Athletic, pitchers in the WC era have made 158 starts on three days rest, their teams won 66 of those games, and they compiled a 4.47 ERA in those starts. So if really good pitchers turn into average pitchers on 3 days, what do you think an average pitcher is going to turn into? Because Matthew Boyd isn't an ace. He had a 5.51 ERA in his last 9 starts or a 4.63 ERA since the ASB.
Yes, the Cubs very easily could have lost this game starting Rea or Assad. But starting Boyd was a bad decision and it backfired as poorly as possible.
Also, the fact that a SP wasn't on the WC roster doesn't really matter than much. It was a 3 game series so of course a SP or two is going to get left off.