I have once requested folks to share opinion in this post:
Another new event on Android - Tree of Choice!
And many ppl wrote there with negative comments. But many was happy, cause they got what they wanted from there with one run.
Personally i do like this event, cause i got Rambard and Bloody Marry from that event (yeah, and HS also, but he is not dig deal) and many good insignias like SL, Empower, Survival. Therefore i can't agree with your "trash and gems-killing event".
Right now i do know i will not participate this event again, since i think i will have to use lots of gems to get last 2 event heroes i am missing. Maybe if there will be 2 EHC i will participate again.
I can agree that cost is high, but it is for all items, not for one only like Event Hero Card. You are taking all rewards which you want (and you select) so count again if up to 16k gems is worth for ALL those items. Of course if you don't have luck you may end up with HS + Warden insignias, which still have some uses, but those are not SL, Empower for sure which i guess you want. You should also expect best rewards will be last, not first. Otherwise you will react like now, cause you hoped you will get Event Hero Card and insignias in first 2 shots, while i think there is really slim chance for that, and it is better to think if you will get them as last, or almost last. So if you want only Fox or Saintess than better don't participate this event. Cause it will not end on one card for sure. Especially if you don't have too many gems to "waste"
But I am wondering what you would tell if you found Rambard or Fox and SL+Empower 10 insignias. Would you still consider those rewards as "trash" ?