Do you know for sure that these are the designs in question?
Can you provide the source?
I would have to agree that the frames shown here are nothing alike.
Monster's frame is immature at best. The "sturdy" thought you offer to downplay Motovox's design is understood from the "more is better" way of thinking.
Fortunately, structural integrity is not measured by lots of welds and pieces. An egg, for example, is simplistic in design yet extremely strong and light. Ever try to crush one with your hand?