I completely agree with what Nebetus said about the damage/defense relation. I wanted to write something similar.

The game currently is about bursting, mitigating the maximum amount of damage possible, based on the zone's damage type and completely relying on lifesteal to survive possible bursts. Life regen cards are ignored, restoring mana happens through physical mana leech, there is no diversity when it comes to defense, most people ignore health and simply go for the highest possible defense, because on one hand, there is no place for HP cards when we are so heavily relying on mitigation (1% more damage received can mean that we are insta-gibbed because the difference between receiving damage with 99% damage reduction and 98% damage reduction is twice as much damage received. Health cards are just nowhere near as efficient.) It seems to me (based on 0.1.16 balance) that things got quickly out of hand because of the exponential scaling of everything. Fixed values help you to keep things under control and give the players an easier time to think about possible builds because the outcome is more predictable. If everything stays as it is and everything is a multiplier, it's not only going to become very difficult for you guys to balance things, because once you change something early-game related, everything else that relies on multiplying that value, will undergo a drastic change. But it will also lead to players not being able to theorycraft, but instead, they will have to go through countless error and trial processes to find the best possible outcome. And this is the keyword. Maximizing the resistance against each zone's damage type and trying to push offensive stats to maintain the best possible clear speed is the best possible outcome. You don't use different skills, you pick a single offensive ability that can clear the room (preferably AOE) and you go with it until the end of the game, you don't switch around and try different elemental skills, you simply use something that is AOE ,partially because that gets you the most life leech with a single hit to survive 1-2 hit deaths and because those are the most effective abilities the game has to offer. The real idle-feel to the game would be if based on the zone's elemental type, the monsters would also have less mitigation against a type of element. Make the game less about trying our hardest not to die instantly and more about the way we deal damage to enemies, so we can concentrate more on putting a build together that works in a way we like it by letting us choose a favorite element, clearing a zone faster thanks to this element.

In my opinion, the wisest way to go would be if you guys worked with around 90% static numbers (pun intended) and gave the players a few multipliers at first, then slowly added more and more once the game has established a solid ground over the patches to come. The game starts off so nicely, you get your +1 damage, +10 health, +1 mana gain on hit. You actually feel like you are definitely progressing, cards level, they gain extra +1 +2 +5 +10 stats, this is the way things should scale. Then all of the sudden, the game introduces a +30% damage card with +5% damage / level and things get out of hand sooooo quickly. Give us static number cards, make % based scaling really low, tone down numbers, hell even toned own XP required for each level and XP gained for each level, so we the browser can handle the numbers and we can go above level 2000.

TLDR.: remove multipliers, give us static numbers.