That's the one for Legend right? I got it done relatively quickly by loading into Skywatch, making a bee line to the cave under the helicopter for the ogre that spawns, kill him, pick up anything he dropped and repeat. Sometimes he'll burp out two engrams at once which is cool. I think it took me about an hour/hour and a half of just doing that over and over again. If he doesn't spawn just reload into skywatch and try again. Awful triumph.

Activities have their own pools, plus open world pool, plus primes etc. Base patrol has a set amount per number of points, points are given for kills, yellow bar kills, ability kills etc. Best way to do it is go every day at reset & play for 30 mins, you're due a new daily prime, kill yellow bars, do the pub event, & kill the HVT bit don't open the chest as it often rewards a legendary gun & this counts for your engram due, but not for this triumph. Dont forget the yellow bar ogre who spawns down below.

I did it by making sure I load in with no other guardians so you can kill everything. Took about 2 hours.