If you read this,
https://bmw.spoolstreet.com/threads/bmw-dct-information.2950/
It explains that(on the M3 at least) that the water to oil cooler is engaged below oil temp of 95 deg C.
This is actually to warm the oil, not cool it.
Above 95 deg C the Oil air works. The reason a lot of coolers on non M vehicles are ineffective is because i dont believe the thermostat is taken into account on these installations. On the non M there is no “cooling” other than what the water to oil can deliver which is less than ideal.
On an M3 however an upgraded cooler itll work because it has a heating AND a cooling cycle. The secret is the the thermosat and its bypass network.