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You write "setting of 14.5V -14.8V will never damage the AGM battery. The charging current will be reduced to very low values". How do you think charging current is controlled if not via lowering voltage? You would win Nobel prize if you would be able to lower current through the battery while keeping high voltage on it So please learn some basic physics first as you are confused. Yes, it will drop as battery charges, but after certain point it will just be heating the battery and heating battery will begin increasing current.

Regarding constant voltage AGM charge mode: yes, there is such. But the charge should terminate when the voltage stops increasing over time. This is not possible to monitor while battery is in a car, because voltage is always changing as electrical consumers are switched on and off.

If you keep 14.8V without current monitoring the battery will not die immediately, but it will certainly not help its health.

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You also write:
- "the current can not exceed 0.1C": this was correct like 30 years ago. Modern batteries can easily handle 0.2C and even up to 0.35C (as stated in that picture). And even much more when battery is deeply discharged. So fast chargers are designed for modern batteries and do nothing wrong as long as they are quality ones and monitor charge current vs voltage.
- "setting greater than 14.9V will damage the AGM battery": again, depends on the temperature of the battery, this is only valid at 25°C.
- "The battery in the BSD system is charged only up to 60-80% of the capacity": yes, but only because car stops increasing voltage above 14.0V when battery is sufficiently charged. And this is not to keep it undercharged, but for the specific purpose of not to heat the battery (my educated guess).