Notice the blockiness of this gundam and see how a g1 figure would be possible.

Imagine this Megatron concept art as a 15inch figure that still has good articulation and detail. Gundam models are easy to customize so you can add more details like panel lines, more paint aps, etc..

Also, bigger characters like devastator and menasor could also be done the same way. I think the key to making a good G1 figure is to keep the design simple.
Take a look at this combiner wars menasor figure. Now look at the concept art of menasor next to it. The combiner wars menasor looks nothing like how he should look. Yes, the concept art is from a video game but it is a perfect representation of a G1 menasor.


Now i'm not gonna lie, the combiner wars devastator looks amazing. The only thing I don't like about it are the arms. The arms couldv'e been blockier, but on the other hand it's a pretty solid figure.

