Thats basically my point. 3600 is an very high amount to get from chest rewards. BUT thats also what it took to get 9 artifacts.
1050 might be mroe reasonable, but it fails to get the artifacts needed. He only got 6.
That is way to wide a margin for a player to do nearly everything they can, and still fail pretty badly.
I have gotten 7 artifacts so far, and will easily get an 8th by the end of the event, and while I did not track the exact amounts, I have gotten maybe 1500 essence out of the prize chests so far, and I think 150 once from a VV chest.
One variable is whether you managed to never open the bad value chests, the one where it costs 32 or 39 or 43 essence per feather. Too many of those will kill your average essence per grand prize. With the essence per feather rates of the other chests, you should easily get a grand prize for every 600 essence you earn. So the just over 5400 essence earned from completing all sequential and daily quests would get you 9 grand prizes, or 5 artifacts. Add in collecting an average of 20 essence around the city for 26 days and you have enough for another grand prize. So 10 grand prizes with zero luck getting any from the prize or VV chests. Your 3600 give you another 6 grand prizes, on average, which makes 16 grand prizes, or 8 artifacts. So you somehow squeezed out a 17th grand prize for that 9th artifact, meaning your essence per feather average was closer to 26 or 27, and a higher ground spawn average, since we still have another 12 or 13 daily quests to go, meaning over 400 essence to earn that is not part of what you have already done. But if you average 26 to 27 essence per feather, that is 520-540 per grand prize, or about 8800-9200 essence to earn 17 grand prizes/9 artifacts. So yeah, your numbers add up for where we are in the event timeline. You should easily get one more grand prize by the end of the event, or two more if your luck with the chests keeps up.
TLDR version: if you want 9 artifacts and do not want to spend any money or diamonds, you need very good luck and need to win about 3000 extra essence over the course of the event.