There are some edge cases where secondary stats can overtake mainstat but as already said above, in most cases higher itemlevel wins (except trinkets and rings/necklace).
I've already seen this several times that players are either misinformed or take secondary stats way more important than they usually are for their class/spec, does someone know where that thinking came from?
Like, optimised secondary stats will make a difference of course on the same itemlevel but for most dd's i'm aware of it won't make the difference of someone being able to do 20% or more damage than before, the effectiveness gap, diminishing returns and the natural distribution due to how gear works and there being no reforging won't allow that.