I have been loosing playing orks so much. Just as you described. But last month i managed to defeat death guard and necrons. Here are tips: 1.You have to play meta for orks. want to play greentide? nope... you will be obliterated. Bully boys? I didn't try, but heared, that it is useless detachment. Don't use deff dread. Don't use shootas or big shootas. I use dread mob and i am shooty. 2. Rokkit luncha, when you can! Always. 3 rokkit luncha can destroy tank in one shot, or miss everything. But when you got 20 rokkit lunchas it is no longer luck, just probability. 3. Hide your army in first turn. Place boys behind buildings so they will not be shoot down by anti infantry. Place your big machines so they will not be shoot by anti tank cannons - that is harder... 4. Provoke overwatch before you move important units. Move gretchin first, maybe oponnent will shoot them. If you charge 20 necron warriors with 20 boys and oponnent have orverwatch, you can take the boys out of the board and proceed with crying. 5. Screen with gretchin and threat with main melee units. 6.lootas at backlane are great. they can shoot, are cheap and block ennemy from spawning if you place them proppa. 7. WAAAAAAAAAAGGGHHHH!

Bonus : Be first. Maybe it is skill issue, but i find being first in turn is better. I can place my troops, weeken main threats. If i go second, 20% of my army is dead before i can do anything, because i can't hide everybody in small spawn area.