My average is making it to round 5, I sometimes get to 6, and once got to 7. I've been able to win at least once with all hands I've drawn, even ones with more bronze than silver and gold. After using at least 20 vouchers, I am thinking the biggest mistake anyone can make is while they're picking cards, they pick ones that don't pair well with the cards that they've already drawn - getting an excessive amount of golds is just a handicap, and in a way can work against you if you think you're... golden.
As a side note, I wholeheartedly disagree with the players saying that Arena mode success will eventually depend solely on RNG. First off, it's not left up to RNG when you get to pick the cards as they're drawn. Granted, four cards at a time makes it difficult, but the lax restrictions on card quality and faction are fair trade offs.
You also get to determine how your cards are played. So really, the strategizing begins when you pick your cards. From there on, your success highly depends on everything you do... or don't do. And, yeah, it's really hard at times... knowing how to navigate a round when you're not able to determine your opponents strategy from simply observing their leader and the first few cards they play. You can't rely on prior experience and knowledge of common strategies, instead you have to be actively adapting to the current situation and modifying your strategy after each card is played. RNG is a very small part of winning.