‘scholar’:
Being 'near' is not good enough for it raises ambiguity. Zechariah does not say that the 70 years of fasting is reached in Darius' 4th year but only that he received the vision in that year referring to 70 years in the past. That is your problem.
No problem for me whatsoever. The author could have chosen the year the temple was actually completed and said 73 years, but this would lack the favoured use of the number 70 in Jewish literature. Your claim that Zechariah only ‘received a vision’ in the 4th year is entirely contrary to the passage.