First of all: I dont move around like Superman swallowing bullet after bullet. I really avoid getting hit.
I am an average player, but when they call for backup and this technical pops up on my back out of nowhere firing at me along with 2-3 Peggys plus this heavy armored machine gunner i wonder how others react inh this situation.
Yes of course always throwing C4 at the pickup is the solution for everything yeah but what if you dont have explosives? Throw Smoke? Run for cover?
As quickly as you can in the game, do a lot of side missions and get prepper stashes so that you can buy the sniper rifle with silencer. OR if you are good with bow and arrow, the trick is to sneak around the cult places and shoot to disable all of the alarms without being seen. this takes a lot of patience, but I've been able to do it throughout the game.
Another tactic is to get a helicopter with missiles as soon as possible. You get 4 rounds of missiles before you have to spend $1000 to replenish. If you aim quickly enough, you can blow the alarms to kingdom come before they call for backup.
I agree that once the alarms are triggered, it's a nightmare - people pop up from out of nowhere, helicopters appear from nowhere and start pummeling you with bullets, and before you know it, you're dead.
IF you do trigger the alarm, you can press the menu button (Xbox One) and restart from the last save point. That gives you another chance, although it may start you at the other end of the map which is annoying.
Hope these tips are helpful.