When i saw that trial requirement, i too was stunned. I am approaching 2 months into this game and i couldn't clear legendary trial 2 too. My gripe is this event is pretty much newb-unfriendly and a departure from the style and requirements of the past few events. I've heard from a friend whom has played the game since shortly after launch that there was only one event in the past that couldn't be cleared by heroic difficulty, the one that introduced Kahuna. There too were many complaints about it and the events thereafter were 100% possible to complete by heroic. This event basically requires you to be able to clear the legendary stage easily (complete quest <=7 turns, clear with team of 4, and 50 Tristans who only spawns in legendary and master) to be able to attain 100% completion.
Yes, the common argument against this is "you are a newb what did you expect? heroes to rain down from the sky?". Bear in mind this is an event, not persistent content, surely you want to make it as accessible as possible? In making it so difficult, only seasoned or p2win players could fully clear the quests and net a free Tristan and go on to add to the cancer that is this game's arena, while the newbs struggle and get little to nothing.
I was close to quitting the game because I couldn't figure out what the devs were thinking when they implemented certain stuff and mechanics, this event may have been the nail in the coffin for me. Feel free to flame me. Peace out.