You people and your spreadsheets.
If you're at capped magic haste, appropriately geared and WS'ing as quickly as you should, if you happen to be the only DD, every other Rudra will produce darkness. The more DDs, the percentage of self darkness SCs will decrease proportionately. WSDmg will increase both the WS and the SC damage.
Furthermore, we already have 16% crit damage bonus naturally. 1.21 / 1.16 = 4.3. Since we don't have natural WSDmg, it's 4 wsdmg vs 4.3 crit damage.
Put down the spreadsheet and actually play the game already. It's meant to be a tool, not a guide. Gearing yourself based on the spreadsheet is like gearing yourself based on myffxigear.kicks-***.org.