The training is pretty similar. Don't be fooled into thinking that single pilot IFR air taxi work is a "minimum" with airline work being a "maximum". Flying a twin alone in unfavourable conditions (eg turbulence, icing, sick passengers) and making all the decisions on your own can be every bit as hard as making those same decisions as part of a crew on a multi-engine jet airliner with all the kit, flying above the worst weather, and with cabin crew to help with the pax...