U didnt notice Vengeance talent or what?
Even with Nature's Grace and Vengeance Hit > Crit for Boomkins. Why? Well, if you cast wrath after you got the proc, you have 1s cast time and then have to wait 0,5s for the global cooldown to finish. If you cast Starfire instead, you will get from 3s cast time to 2,5s cast time, which is 1/6 (16,7%) more damage compared to a 3s Starfire. But: This faster starfire still can miss and you need to have 6 crit procs to get the same effect as 1% hit (you miss one spell less = 100% more damage on one spell).
CASE A
Now apply that to a standard 2 minutes boss fight. 120s fight length / 3s cast time = 40 spells. Now let's assume you're buffed and have 32% crit, 88% hit. Then you get an average of 11 crits (casts*crit*hit = 40*0.32*0.88), which equals 1.83 more starfires (which also can miss) from the casting speed talent.
With 88% hit you will hit 35 Starfires (casts*hit=40*0.88) of the 40.
So you loose 5 Starfires and gain 1.83 extra starfires.
CASE B
You still cast 40 starfires in the 120s If you now replace 4% crit on your gear by 4% hit you will get 92% hit and 28% crit. Therefore you will have (40*0,92*0,28) 10 crits, which is 1.66 more starfires.
But you've got 4% more hit now and will hit 37 (40*0,92) of your spells instead of 35 the from the example before. So you lost only 0,17 starfires because you reduced crit, but you gained 2 more starfires from increasing hit by 4%.
Just do the math with casts*hit*crit to see how many extra starfires you will get and casts*hit to see how many starfires will hit. Ofc you also have to count crits as "double normal hits" (cause it does 2x damage) and in the end count which hit/crit combo makes most "normal hits", but with these formulas you can do it.
Roughly got what I tried to say?