Slow and Para directly scale with dMND so their similar to Blind II. Additional merits just add static percentages onto them, its the equivalent of tossing on more MND and allows for a slightly higher cap. Para II also seems to act differently the Para 1, notably on NQ monsters or regular NM's (the non super resistant kind). When I'm doing campaign or just solo work I can easily tell the difference between Para 1 and Para 2 (2/5 currently), it's not a placebo its a real noticeable difference. Of course on anything that actually matters Para II is complete sh!t, but that's SE for you.

In all honestly all of them except Dia III are crap, SE deliberately made them weak to prevent any more "Avesta" situations.