The easy, familiar, can build with jellybean switchmode parts approach to a charger is to build three single phase isolated converters and wire them star. This is because a 230V switchmode supply is a very standard thing and there are a LOT of off the shelf and high volume parts designed for such use.
Going delta increases the PFC output bus voltage (because you now have 400V RMS, so you need a PFC output north of 565V) which is out of reach for the common 400 or 450V caps and probably too high for the common mosfet choices (And you still need to build three of the things). Yea the primary current in each converter is a little lower, but the need for more expensive switching and bus caps probably trumps that consideration.
Now if you are going for a star connection, then you either need to ensure you have perfect balance and no triplen, or you need a neutral. You can of course use a synthetic neutral but that is quite a bit bit of iron, and you really don't need that weight on the vehicle, better to do that (if it is even required) on the shore side of the cable where its weight is not hurting range and acceleration.
Seriously, in the scheme of things a few amps or even a few tens of amps of triplen and imbalance is just not that big a deal, and is far easier to fix in the land side transformers then it is in a weight and size constrained mobile environment.