Regarding offhand bonus - the reason why the bonus is not really useful even for rogues is because it only affects how much damage white hit from offhand makes and since that value is small in the first place adding few more percent on top does not make it better. All skills are based on main hand doe weapon, that's why offhand is pretty much stat stick.
I suspect in the past when skill percentages were not as high as they are now and when white hits were comparable to skill hits that set would be good option to consider but right now the bonus is pretty much useless rogue or no rogue.
I really hope they update and include crit letter set similar to chain, I will be delighted if offhand set is no longer droppable but not another way around .