I think the experience gap is way to large. Instead of 35-45 night exp for USN and 75-85 night exp for Japan, it should be more like 50 for USN and 60 for Japan.
I went through a few ships to compare day/night experience values from a saved game versus the AI. The date is 6/2/42.
Here is what those numbers are:
IJN-
BB Yamato: 68/67
BB Kirishima: 66/74
BB Haruna: 65/65
CA Tone: 77/65
CA Atago: 74/74
CA Mogami: 75/73
USN
BB West Virginia: 71/48
BB Nevada: 70/55
BB Arizona: 72/44
CA Vincennes: 74/55
CA San Francisco: 73/39
CA Indianapolis: 67/50
RN/RAN
BB Prince of Wales: 69/72
BB Warspite: 67/77
CA Australia: 71/45
CA Canberra: 67/47
I simply chose whatever ships were listed first on the screen.
The day values are very comparable overall. The night values are considerably different but not so much so that its unrealistic IMO. The Brit BBs are very experienced in night action, equal to or better than the Japanese. It is interesting to note that some ships are better night fighters than day!
Chez









