True, another option to find the space for the World Fair building. Six SOKs would require more aids than 1 Terrace Farm, but SOKs given the priority list likely get the aid needed, if not there are always the Self Motivation Kits or Mass Motivation Kits to fix that. However, removing 6 SOKs reduces 6 FPs then replacement with the World Fair will represent a gain of 3 FPs /day.
Replacing a Terrace Far for a World Fair represent a gain of 4 FPs (9 vs 5), plus also a gain in space (24 vs 30 tiles). That extra space gain could be used for an additional SOK or Sky Watch, then net gain of 5 FPs/day.
It all depends on what is available at the city, which buildings be at the chopping block.