Strafing was removed to make the controls simpler. In the early development state there was steafing but moving to side while looking at the target was awfully hard in 3D perspective. Also not having strafe made the game more fun as you have to control the altitude and choose between facing the target to attack or focusing on avoiding in combat.
The countermeasures are automatic in this game like tiger's bane, assuming the co-pilot is controlling it.
When the enemy AA missile is launched you must fly away from it. When the missile is close to the helicopter you can see the flares launched from it. Doing a quick turn after that will outmaneuver the aa missile.
I changed it because using flares in Steel Alcimus was a chore and spamming it while hovering to avoid missiles were kinda dumb.
In this way not only using countermeasurement is more convenient, it also looks more realistic as you must perform evasive maneuver to make it effective.
Your helipad don't have defences because players could abuse it to take down enemy aircrafts easier. You don't need to protect your helipad in this game and enemy ground forces don't attack you when you are landed in 1.8.0 patch so having no defence isn't a problem.