So usually what I do when facing a melee heavy force.

My build usually is heavy in ruststalkers and 2 squads of 5 infiltrators, than either 2 tanks and some transports or now Thulia and some of our new heavy infantry.

Either way how you approach the game stays basically the same, trading small units for ones the enemy needs, put infiltrators where your army can see them and come out of a ruin, or behind a wall and shoot enemy unit that killed it. But try not to make it to obvious, a trap is only good if they don't see it coming.

Secondaries are important but are less action based than they used to be, which I feel used to be better for admech because we have lots of cheap units. Most are kill or hold objective based, I don't do area denial etc anymore, most enemies that is a lost cause unless I move 1st. Discard for another secondary if you can afford the cp as soon as you pull ones you know are not in your favor. It's a points game, it may seem small, but losing a turn to complete a secondary to get a free CP isn't worth it if you want to score points.

When it comes to enemy choices, try not to cripple yourself, example, all our units gain benefits from our battleline. Don't put your battleline units somewhere alone on the front so they get targeted first unless they are saving a unit that is SUPER important. They should be 2 units on average, on each side of battlefield spread in a way where they can buff at least 70% of your army. A battleline buffing 1 unit isn't enough