Luck Tonic gives +4 Luck, not +2. So with Potent Potion it becomes +6, giving us effectively 91 Luck.
Throw in a Rally Luck (+8 Luck) and that becomes 99.
At that point, might as well go the extra 1% for a guaranteed activation.
You can use Rally Spectrum (+2 Luck), build the last statue, hold a Visitation Seal, whatever gives Luck.
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Miracle build is for battles. Gold build is for grinding. Both have an entirely different purpose when compared to each other, so it seems pointless to deem a "better" build in my opinion.