Why is 纔 the “correct” traditional form of 才?
纔
Due to the complicated strokes, the traditional form 纔 is being wholly replaced by the simplified form 才 even in Hong Kong and Taiwan.

I was from Hong Kong, no one would use 纔 instead of 才. Just look at how many more stocks in 纔 compare to 才. I would consider 纔 is the archaic form of 才

Why is 纔 the “correct” traditional form of 才

It was the “correct” traditional form of 才 but now is archaic (almost no one use it nowadays).  才 is officially the standard (in traditional or simplified Chinese) in modern Chinese. 纔 had became a rarely used variant (it is not incorrect but it is very old fashion)
BTW, the argument in the text you posted is about &quot;We shouldn't insert modern concepts in ancient language&quot;. If it was written as 纔 in the first place, just leave it that way