Mmh… maybe I’m misunderstanding, but based on what I’m gathering, here’s the best answer I’ve got:
When you’re fusing pets, they take the average of the two pets’ abilities for each of the three categories. You have a higher max level cap, but you will potentially have more ground to cover, simultaneously costing more fame. If you like the first 2 abilities of your pet, definitely make sure those are both maxed, at least, as it sounds like you are doing.
The real question is, how much do you actually care about having decoy? If it’s a low priority, then I wouldn’t worry about maxing them, unless you plan on getting a 100/100/100 pet relatively painlessly. It’s a matter of preference with with time/convenience trade-off.
I hope that answered what you were intending to ask. :3