Sure. But that's assuming you'll only be using those skills once per dungeon run. If you've maxed-out your first monster's skill down to a 5-turn cool-down, you'll likely have times where you activate its skill twice or more in the same run. If you only raise your second monster's skill to a 6-turn cool-down, you're only decreasing the frequency with which its skill is available to use.
For example, turn 5 comes up and you pop your first ADK's orb change skill. Now he's back to 5 cool-down. Turn 6 comes up and your second ADK(skill cool-down only improved to 6) activates and you pop that. Now the first ADK's cool-down is at 4, while the second ADK's is back to 6. Now you have a 1 turn gap between your two ADKs' cool-downs. A third cycle will increase that gap to 2 turns, and so on, until the first ADK completely laps the second.
Another popular example that people actually use are triple Echidnas. The constant time-stop loop requires all 3 Echidnas to have the same skill cool-down.
Now, this won't matter all the time, but my point is that maxing-out a skill is never detrimental, and purposely staggering skill levels is not better than max skills in any way. It's a wash at best, and can mean defeat at worst.