To me, what you describe as 'not Roppongi' sounds incredibly plush. Mr. Baseball was plush. In Tokyo I shared a three-bedroom apartment with three others, and also lived in a gaijin house for a while. But most of the time I lived at the Kimi Ryokan, sharing a room, and of course with shared showers, toilets, etc. Air-conditioning? The idea of a $3000 housing allowance? Teachers got, and still get, 250,000 yen per month, no housing allowance, and you usually had to come up with the non-refundable key money on your own (an exchange rate of around 120 yen to the dollar). We lived on about 2/3 of what you think is a minimum housing allowance. It's especially interesting since Japan has experienced deflation since then, and the cost of living is now lower.

While there may be a middle tier of expats, from my point of view there wasn't much difference between the middle and the upper, because they were all incredibly luxurious.

Equivalent housing to home is a luxury.

Whether you are in Roppongi or not, if you come over on an expat package you live in a different world than the ESL teacher.