"28c in the offices in a rich industrialized country? I wonder how much productivity they loose because of that."

A lot. The 28-degree "standard" has in fact been in place since 2005, when introduced by now-Tokyo governor Yuriko Koike who spent her younger years in Egypt, and has spread from government offices to almost the entire nation. In winter there is no corresponding artificially-low indoor temperature; if anything, they tend to keep it at 25-26 or more.

Total victory for the warm-blooded lizards and total misery for us hairy folk.

if it's 35-40 outside you don't wanna collapse when you step outside, just because inside office you had 20-21, which actually means free degrees less since temperature sensor is usually on unit at ceiling with hot air

this is 100% anecdotal. But I got the impression that you get used to it rather fast if the climate is consistently hot for a while.

Source: I got used to Bangkok's climate in a month and happily worked with a fan only, without AC