It promotes a game play where for 12 seconds of the game you don't do anything. You run around, making sure that you survive and that you don't cast your spells/skills so that they are not on cooldown when the 4 seconds come in which you can must cast all your skills to do your damage. Do you know what casting skills is called? PLAYING THE GAME. I'm sorry for yelling, I'm very frustrated with many of the developers decisions but for me this one takes the cake. Convention of Elements came to be as an alternative to Stone of Jordan. You see Stone of Jordan was seen by, well everybody, as a very boring item that provides such a damage boost that it was seen as a must play. What is the developers solution to this problem? An item that is far more boring since it promotes that you do not actually play the game for 3/4 of the time. The biggest problem is just how powerful it is; To a point where you feel like you are forced to play it and there you are, casting your skills with almost no damage most of the time, feeling frustrated and then finding that "oh wait, my skills are on cooldown now that the element of my build has come up, ups, I guess I'll wait for 16 more seconds to be able to do anything" or, you can have the joy of just running around, not doing anything but trying to survive because it's not your time to play the game.
Yes I am frustrated. Yes I am angry. Diablo 3 was in development for 7 years and it has been 5 years since it is out. 12 years should be enough time to make a game that is fun to play. Many of you remember the state that it came out in, so I won't say that progress has not been made, but it sure seems like it has stopped. And there is so much more to be angry and frustrated about. So why am I writing this? Because I love the game. I have spent a stupid amount of time playing D3 and I will most probably keep on playing it, but something has got to happen to make this game fun again. Things like Convention of Elements and Set Dungeons are just not fun. I won't go into Set Dungeons so that we stay on point and topic. Games are suppose to be fun and somewhere along the way when the developers were brainstorming for things that are new and unusual they forgot to ask themselves if those things are fun.
Please remove or rework Convention of Elements, sooner rather then later, not an year from now, that is very much too late, do it while there are still people who enjoy the game. Thank you for reading. Try to forgive my anger, I would not shout if I did not care.
EDIT: I agree with what a lot of people have stated, don't remove or rework Convention of Elements. There are people who actually enjoy that play style. These people are clearly mad, but they too should enjoy Diablo 3, but I digress. Instead we need items in the ring slot that can be placed in the Kanai Cube, that are of a similar power level to CoE but different play style. Preferably a play style that does not cause 80% of us, judging by the response on this thread, to be bored and frustrated.