Different lists have different needs. If you can kill all of the enemy you do not need scoring units [wipe-out victory condition], which granted is hard to do. If you can contest all of the objectives the game goes to the highest VP scorer [not as hard to do as wipe-out, but could still be difficult].
In 5th I would say this is what you should consider as mission objectives in every mission:
1) The Scoring unit vs KP dynamic
2) VP acquisition/VP denial
3) Sheer destructiveness
4) Planning against Phase-Out [though this generally doesn't contribute to victory]
If you can win on point 1, you don't need to worry about the others. Same on point 2 and point 3. However, if all 3 are available, you have 3 different ways to win. I throw point 4 in because as a Necron player this victory condition is available to your opponent.
My lists generally don't go over 20 warriors in 1500pts and I've never been called cheesy or unsportsmanlike, because I play a CC list that really needs stuff other than warriors. Also, it is vulnerable to the opponent phasing it out. In 5th edition, I'd say for now it's more important to protect your warriors, which will prevent phase-out, rather than field more of them. You can always place them on an objective in turn 5, where their durability will help them survive the chances of random game length bringing extra rounds.
Different approaches require different unit selections.
