WHAT!?!?!?!
If you're separated from a buddy, you NEED a redundant air source, since one will not be available. Twin tanks completely fit that, even you stated this when mentioning solo. This is really basic stuff, please stop misleading newer divers who might be reading this.
Agreed, that makes no sense. You don't need to be stronger - just have a better speargun or sharper dive knife!
Rob