Hello Rick,
I would not rely on weight as a reliable indicator of subwoofer performance. For example, some of the cylindrical subs are made of cardboard--variations on the sonotubes that are used as cement formers, and they are capable of excellent performance. The round shape nicely inhibits internal resonances without the need for heavy bracing material.
The basic laws of physics can't be ignored in conventional speaker or subwoofer design: enclosure volume and driver diameter being two of the crucial factors. Also the design: servo-control and feedback, while expensive, can result in subs with remarkable bass extension and output (some costly Velodyne and Paradigm subs).
How a subwoofer radiates low-frequency energy isn't all that relevant, whether down-firing, front-firing, etc. It's just energizing the low-frequency room modes. Placement within the room, plus the factors above, are far more influential.
Regards,
