Is The Overall Weight Of A Speaker Important?

"they claim excess weight just stores unwanted energy"

If its unwanted energy wouldn't we want to store it someplace? If it is not stored where did this unwanted energy go?

Multiple English speaker makers have done an excellent job of using the box resonances from light enclosures to augment the bass output. The box resonance is "tuned" very much like you "tune" a port to be a positive addition to the overall frequency response.

Not much can be determined by weight alone other than how many people needed to lift.

You're welcome, Rok2id. I think that the takeaway here, if you think about it is, speakers are part of a system, which includes source, switching/control, and amplification at a minimum, in addition to the speaker. In a very important way, the system also includes the listener, the room and the software. The "perfect" or holy grail speaker is likely to be somewhat to very different for each and every combination.