My comments are only contradictory if you want them to be.
The G3M and G4M are clearly different planes but they had similar roles.
The G4M is a plane developed by the same company that was intended to be better in every way (except possibly range) than the G3M.
As such it is the G3M Extra and explains why the G3M was not further developed.
The Ki-15, 46 and the latter Nakajima C6N are unique planes in that they are dedicated reconnaisance planes that were designed specifically for this role with no compromises to give them any multi role capacity. As such they are examples of a Japanese trend to design planes that were optimised for specialist roles or even for specific niches within that role. A focus on maneouvrability and range was common and resulted in planes that had incredible abilities and just as marked weakness. To achieve maneouvrability and range many designs were very structural light and not over supplied with engine power which restricted the options to redesign them later to widen their scope of work.
By comparison the Mosquito was initially proposed by de Havilland as a powerful unarmed fast bomber. The provision for forward firing weapons was included in the initial design by them to increase versatility, critical given the lack of support the concept initially received from a conservative Ministry. A reconnaisance role was initially forced upon the plane by a Ministry sceptical of the concept of a bomber with no defensive weapons.
By planning and by circumstance the Mosquito was conceived by de Havilland as a multi role plane in a way that Japanese planes were not.
Perhaps the environment in the UK gave greater freedom to designers and companies than was available in Japan as the Beaufighter was also a company driven design that was intended to achieve multiple roles.