Capital only multiplies productivity of labor
I think you are quoting Smith out of context. Capital does multiply the productivity of labor: if and only if that capital is invested in new capital equipment.
The use of capital for the creation or purchase of capital equipment in turn requires the use of additional labor thereby having a direct stimulative effect.
I don't have Smith in front of me, but I can't believe that he believed capital in in of itself was a negative or a non-important factor relative to labor as you have presented it here.
In fact if my memory serves me, Capitalism was somehting Smith promoted vigorously.
I think you are just someone with a political axe to grind. As such I wouln't take your economic theories with anything more than a grain of salt.