I'm pretty far with progression of my sin.
For weapons I went: Random rw -> Lo runeword -> Lo runeword in sacred knife -> tracker set knife -> Lo Xis in eth sacred knife
While you can sustain mana from knife procs, from either tracker set, su or craft, vs single target, bosses, bosses in rifts - not gonna be enough. Lo xis gives you enough mana sustain for bosses, good damage, (runeword ed and +150 damage average, 40 slows target, some reanimates).
Thing to note here is, knife procs are 50 wdm, no bonus magic damage. Maelstorm spikes are 80% wdm, converted to magic (-40% res from doom), and they get +magic damage bonus, which can be over 10k with high endgame dex and hexward shield. In other words this makes them way stronger than knife procs on gear. It is not same scaling as old builds that relied on ways damage and procs, ways are very weak in comparison to magic damage you get from maelstorm skill dex bonus.
You end up throwing maelstorm and each spike from maelstorm deals for example 3x more damage than those knife procs you see.