So, after months of trial and error, I finally managed to get a team together which can beat UDK about 60% of the time, depending on the other team champions. I flit between gold I & II. I still don't have that champion myself, so no, not everyone has him.
The key to beating him for me was when I got Mistrider Daithi. Other champs I use with him are Helicath, Yelagirna and Seeker. I have Ronda, but no matter what other champs I paired her with, I found her of little help against UDK. Her blocks helped, but being the weaker affinity, she just didn't hit hard enough against him to be worth it and my team got op pretty fast.
Now that I can beat him most of the time, I still hate going up against him in arena. I still see him in about 8/10 arena teams, and some of the fights, depending on rng I can go make dinner, come back and the fight is still going on.
I've been playing about 5 months in total, so still have a lot to learn, and I know it, however, facing UDK in almost every single game in arena almost stopped me playing completely as it was so frustrating.
My champion roster isn't that big, Ronda, Hurndig and Warmother are the only other legendaries I have besides Helicath. I have around 20 epics which consist largely of support champions and healers, no really good dmg dealers and I'm still working on masteries, gear, ascension and blessings etc for the champs I've levelled.
I still think he's OP, but while I did have the patience to persevere, I'm pretty sure there are indeed a number of players who have stopped playing the game because of that one champion - the one friend I did send a link to did exactly that (my former RL in WoW), so while he may have been a novice in this game, he does come from a gaming background and not just the game I mentioned.
Just my 2 cents.