I don't really understand decimator damage

[Escroteitor]

I was trying in the VR training as a TR comparing it with a AI grounder.

First I shoot a max with it. He didn't instantly died, I was kinda shoked. I though max has 2000 health and 1 decimator rocket should bring him down.
After the decimator rocket I unloaded 25 bullets from a MRW (143*0.2*25=715)
I don't get it, or the decimator isn't doing 2000 damage to the max suits, or they have 2600 health
Looks like I can bring down a max with 2 rockets from both weapons.

I tried it with a liberator, 2 decimator rockets kill the liberator. 4000 damage.
Then I pick up the grounder, and fired 6-8 rockets to the liberator to kill it (at least 9000 damage).

Then I shoot a vanguard in the back with the decimator. As far as I can remember I needed 4 rockets to bring it down (8000 damage). Maybe I'm wrong but normally I just need 5 grounder rockets to bring it down (7500).

The last one is the only one that makes sense. So I don't really get it. A tradeoff of about 50% speed and a rocket for a 30% damage increase.

Maybe the VR training is not registering it properly, why you guys think?