@bghazzal agree with what you say.
Mic21 can be expensive for imported dive gear, but strobes and some accessories are a lot cheaper than Europe. My wife allow manages to pick up decent beachwear cheap and got her snorkelling kit there as masks etc fitted better and are prettier. Some of the dive computers were decently priced but some were expensive. A diver friend with a japanese wife picked up all her kit there as it was difficult to get correctly sized kit in Europe but she got a mix Gul and Western brands
Like you say the golden days for Japan was the 80 and 90's for new camera equipment by the 90's it was far cheaper in HK (if the triads didn't rip you off) and Singapore than Japan generally. Electronics have been a mixed bag, generally prices similar but models used to be 8-12 months earlier than europe however this gap has reduced and apple products are more expensive than the States.
The second hand market is very different and I still think there is value there compared to Europe and the quality/ choice is very good
So much of whether Japan is cheap is dependent on FX rates and converting from GBP in the last few years has been awful, but is getting better, it would be great if it would weaken by another 10% and then with the sales tax rebate it helps. The OM-1 set up I was looking at is about £500 cheaper if I buy lenses and body second hand in Japan than second hand in UK and £1200 cheaper than new kit.
The exception like you say is housings, these seem to have global pricing bar ikelite which is slightly cheaper through backscatter. So if I go down the Nauticam, Isotta or Aluminium route then I will be trying to get a deal of UK shop
I think the internet and visibility of pricing has ruined a lot of the pricing arbitrage across may sectors as it is definitely closer than it was, however there are still bargains to be had in sectors. I have a penchant for Japanese denim and that is 50% cheaper in Ueno / Harajuku then I get in London or the USA