As the pvp system now stands, getting experience and levels is bad because with levels you'll get increasingly harder pvp enemies. Optimum way to play now is by automating missions and avoiding leader exp, while hoping to get better equipment and resources to make the compound as well fortified as possible with lowest level possible.
True, you get harder PvP opponents, but you also become a harder PvP opponent, as long as you use the newer weapons you find. But you won't be a hard opponent if you don't have great strategies. People automate missions, because they can do more in less time, thus giving them more items. Items than can make a difference in raiding/defense. A part of why they also do automated missions is because of what you said, but it's not the main reason
There should be a way to handicap defenses and player gear in higher levels to make them eligible for lower levels.
My suggestions for handicaps:
Highest equipped gear level on any survivor + leader level / 10 = allowed minimum level targets for the player.
So for example lv50 leader could equip his survivors with max lv10 weapons/gear thus allowing him to attack lv15+ players.
Maximum incoming attacker level should also be limited when the player is using lower level gear for defense. Maybe the same limit as above.
I am very confused at what your trying to suggest. Are you saying I should wear items that are much lower level than I am, so that I can raid other players that are much lower level than I am? This doesn't make sense at all. Are you that bad in PvP that you decided to make this very strange idea? I would suggest getting advice on how to be a better player in PvP, than whatever this is. Using much lower level weapons than ones actual level can backfire on you when it comes to zombie raids.
This way getting experience and levels wouldn't be a bad thing.
That's your opinion. Some people want to level up, others don't. Like you, for example. But it's not a bad thing, trust me. You're just having difficulties with other players that have been attacking you or that you have attacked. It doesn't mean make ideas that are very strange so that you don't have to face harder opponents. I recommend you change your strategies. It's the best that you can do. If you keep having troubles, get a White Flag book and opt out of PvP for good.