Pfft, the Rock is ready by the end of 1998. This was about continuing to build up HHH.
Unlike the haters out there I think what they did with HHH in late 1999/2000 mainly worked...just not that match. He'd just been through an absolute war with Foley earlier in the year and the wet fart way he wins this match.
Show was the fourth wheel. If it had just been Rock and Foley and HHH though the match also wouldn't have worked. We have tons of proof that just Rock/HHH would have worked out fine, but they wanted to reward Foley and making him ref just wouldn't have felt right either.
This is completely ignoring the fact that Big Show actually won the Royal Rumble by the way, so they decide on the four man elimination match with a McMahon in every corner. Honestly? The set up is fine. The match is just a dud with a bad ending.