I don't say it's not a very strong one, but it's a rather dull and contradictory one. Dull in that you'd best use it for Great Persons two eras down the line (as all the other bonuses are not able to be calculated since you'd need to keep your religions balanced, so they're essentially random and can't flow into your strategy), and contradictory since the Garden gives Great Persons the regular way...
In essence, you need to be very adaptable with regards to your strategy when playing the Indonesians.
PS: The comparison with the Mosque doesn't work since that wonder is designed to make your own religion supreme thereby eliminating other religions and thus the candi bonus.
(That's why I guess the
bonus is so high, because it's hard to achieve)