The thing about quality is that it can be very subjective. Diecast feels good in the hand and heft is just something we seem to naturally associate with quality, at least in terms of collectibles. You have to consider that the G1 is also a bit of a brick. It's solid in part due to the materials of the time being of a higher standard than what is used now, but also in part due to the relative lack of articulation. Obviously a figure that can barely move is going to feel much more solid than one that articulates. When articulation is taken to the extremities, we get rickety figures with a lot of give in the joints like modern day mps. Trading off solidity for articulation is just unavoidable.