Relatively new player here, been playing a few weeks. At level 22 so I still can't get anything meaningful out of events or coliseum but here is my perspective:
It is a pay to win game and you made the right call by having two currencies. One free and one paid. It is a common tactic to create multiple bottlenecks and encourage impulse purchases. But why aren't you utilizing the premium currency effectively? Every transaction from the shop from a common girl to a mythic is a separate credit card transaction. I'm sure visa charges a fee for each one and it discourages customers from buying. Instead do what nearly every other game in this genre does; make the primary credit card transaction premium currency and then use that for all in game purchases. Fewer fees, players will blow through it on impulse and speed ups, and you can set the amount of gems larger or smaller than the price of premium items to make people buy more. It is a weird scenario where you could be making more money while streamlining the experience of the user.
Give us a retreat button. More often than not the outcome is obvious early in the fight. Especially in tower matches. This only encourages users to refresh to get back to the game faster. Reloading the entire game from the server no doubt uses more resources on your end.
Similarly there are too many screens to pop up. Between tower matches you get a screen for rewards, another to flip over the card, and another if you have gone up or down a rank. If your chests are full a screen pops up, then an ad. Each one with a load time and spinny circle. Most of these purposes could be served with a message in the background, triggering far less delay. Between this, the high user resource usage, and the long animation times I'm surprised there aren't rumors the game is using those resources to mine for crypto and designed to keep the tab open as long as possible. Aside from potentially scaring people off the inability to disable animations also limits the audience as players with low end machines have difficulty.
Is there a reason each tower level hits like a wall? It just feels like unnatural design to go from winning 90% of matches to losing 95% of matches. The power range within a level is too uniform for this to be the case.
Events feel like they are designed only for well established players. Trying to grasp the strategy I bought a mostly mythic deck of the same element, but still can barely participate in coliseum or world boss. If I could get my payment sorted out I'd gladly throw more money at it, but even if I could nothing available looks like it would help me overcome the health bottleneck. Perhaps some better scaling would help here, to help hook new players by allowing them to participate.
Which brings me to my final point, please for the love of god ditch epoch as a payment processor. About 15 seconds after my first purchase I got a message from the bank for potential fraud. Now my paypal doesn't want to go through. Looking through the comments on the better business bureau page for epoch it is no surprise. I wouldn't touch it with a ten foot pole, or at least maybe a prepaid visa in the amount I'd be willing to spend. Which requires a lot of planning and is not conducive to the sort of large impulse buys these games require.