Central ducted replacement minisplits probably are designed with a fixed blower speed to maintain pressure and flow in a duct system to be sure that conditioned air is delivered to all rooms. If the blower slowed down like a wall unit then just the first room would get conditioned.
The blower motor is an inverter/DC motor so it should be much more efficient even if it doesn't vary the speed and with the compressor doing all of the "variable" pumping it's a good compromise.
The blower motor is an inverter/DC motor so it should be much more efficient even if it doesn't vary the speed and with the compressor doing all of the "variable" pumping it's a good compromise.