You're right, regular slow charging is the same as fast charging; it does not work with firmware 151. With the ASUS 65W charger, the charging time is identical with both configurations.
On the battery there are two other points which are not great, the first can be corrected by a future firmware, the second is the quality.
1) in 7h night, without use, AOD activated, airplane mode, the battery lost 15%. So he never sleeps.
At night, it still loses 0% in 7 hours with AOD disabled, airplane mode
2) The battery is not of top quality or the charger is too aggressive, unfortunately this is the compromise with users who want everything, right now and current technology.
From 07/16/2021 to 08/28/2021 the battery lost 670 mAh (or the capacity is far from the 6000 mAh announced). Fast charge has only been used 5 or 6 times.
Starting from 0% at 3 p.m., device OFF, with a device to measure between a standard charger and the rog 5, here are the results.
2000 - 42%, 2500 -52%, 3000 - 62%, 4000 -82%
5078 mAh 100% (green led) 17:10
5330 mAh 100% real (request for power from the rog to the charger at 0) 17:40
Of course in outdoor games this is confirmed, I lost about 1 hour, 1 hour 15 minutes following the 4g signal
Fortunately 60% of the time I use the bypass
Asus, review the quality of the battery or resent your copy of fast charge, or that of the charger
Note: erreur Not 15h 0% , 13h