Spoilers Below
So fighting one Warden alone sucked enough…fight 2 was a little worse…but 3? That was the definition of hell on earth. How long did it take you guys? What did you find worked?
I made a quick little video just to show what worked for me. Check it out!
give whole team incineration cannons, then I used binary rifle / scattershot combo
took me 2 tries after doing that
Only took a couple of tries. Wasn’t too crazy. I would just send blue team to the opposite side of the room from me so I had a clear shot at a wardens back. Incineration cannon/light rifle to the back, rinse and repeat.
Take the grav lift and ground pound onto one of the tallest pillars. Ground pound to the exit balcony. Done 
I just finished the game 10 min ago and that one was a -Yoink-. It took me over a hour but I wanted to finnally beat halo on legendary.
The Warden would stomp Didact.