The Issue people have is thinking of secondary stats in “absolutes”, they believe secondary stats are unshakable, constant in how good they are.
People will say " Secondary Stat w > Secondary Stat x > Secondary Stat y > Secondary Stat Z" and create this illusion that at any point in your itemization it will always be so.
It will go to the point they will value the first two even more than the past the point and often times undervalue the latter two.
Stats aren’t so, they interact with each other, Invest in Crit? increase the value in Haste (As you cast more crits per minute), Mastery (As your pets deal more hits per minute) and Versa (As you and your pets do more casts per minute); Invest in Versa? and Crit value goes up, Haste value also goes up (as each extra cast is bigger) and Mastery goes up (as Pet damage is multiplied by versa and mastery in a Base Damage Times Mastery Times Versa)
In this sense, every secondary stat is “worth it” under their given proportion, this have a number of considerations.
Someone with 15100 of secondary stat rating can easily invest 30% in crit (4635 rating), 27% in haste(4636 in rating), 25% in versa (4635) and 21% in mastery (1168 in rating).
Someone with only 10000 of secondary stat rating (lower ilvl) cannot, and they shouldn’t for exemple try to copy those statlines, as clearly, he has less stats, and to copy 1 secondary stat of the other player will involve sacrificing rating in the other ones.
It’s why you will see some people with sim advicing you to hit a secondary stat of X% in Haste, but for others it says for them to Drop haste from X% to Y%.
In the end, the best advice i can give you about sims is use https://www.raidbots.com/simbot
It’s not only that, Demonology does more player-related damage currently than in 10.0 or 10.1 even without nymue, belor or iridal/spindle, meaning a secondary stat who increase player damage in general grew in worth , while a secondary stat who only increase pet damage lost some worth.