This is a messy business, much depends on the conduction mode of the rectifiers.
Taking the star case, the rectified dc peak is 1.414 times the ac rms. The dc mean which is a more reasonable thing to consider is 1.4 times the ac rms. You have to subtract diode drops on low voltage systems and that adds more confusion.
So yes the dc will be higher than the ac Take 1.4 times your 10.8v ac giving 15.12 dc and loose a couple of diode drops and you have your 14v battery volts.
Current is not as simple as rectifier conduction mode comes into this but with an air gap alternator you wouldn't expect diode overlap so you have the dc current carried at any instant via 2 diodes. The dc current flows through 2 phases at any instant with the 3rd idle.
You therefore have a current equal to the dc value flowing for 2/3 of the time. The rms value of this comes out to something like 0.77 of the dc value.
So you end up with both the ac rms voltage and the ac rms current being less than the dc components.
If you try this with iron cored alternators with leakage reactance you will get overlap in the diode conduction and the rms current is different. I am fairly sure that if you take the IRP connection you will again find diode overlap when supplying high current and this may be why under extreme overload conditions it shows less stator heating ( or is claimed to do so).
You must not confuse this rectified load with the normal power in a 3 phase system where Power is root3 x rms line volts x rms line current x power factor.
Flux