I really like the idea behind this game. You take an idle/clicker game like Clicker Heroes and add strategy/combat to the mix. It was a lot of fun at the beginning as you unlocked new heroes putting them in their ideal positions and switching up your formation as you unlocked new heroes and abilities. You have a great idea, but it hasn’t been fully realized. You haven’t brought out the full potential.
The issue I find with the current setup is that after only playing for a few hours you can unlock all the crusaders and abilities. Depending on whether you want to click or just do passive dps it doesn’t take long to find the optimal formation with your highest dps crusader in the middle being buffed by everyone else. At this point it is pretty much the same thing as clicker heroes.

To avoid this I have several suggestions. First of all, there should be crusaders that do AOE damage. This could varying. For example, hitting the X closest enemies, hitting all enemies, or simply doing splash damage to nearby enemies. This would open up new strategies to make the game more exciting. In the current game (except for limited use abilities and cards) the only strategy is single target. Either you kill the enemies fast enough to keep up with the spawn rate or you don’t and get overwhelmed. There is no in between. If you had AOE damage you could instead have a strategy based around tanking the enemy damage and AOE them down. I really love the crusaders you currently have that heal and the one that reduces enemy damage in the column in front of him. Crusaders like these would be integral to the tank/AOE strategy.
My other suggestion would be to have more meaningful crusader abilities. Abilities that just add straight up % more damage should be avoided at all costs. If you wanted the crusader to do x4 more damage you can simply build it into the levels such as something like every 10 level increment from 1 - 100 gives the crusader 17% more damage. 1.17^9 is about equal to 4. Abilities that only give damage when certain requirements are met are fine and make it more interesting. The abilities should determine the role of the crusader and do things like a heal or buff nearby allies. You can have abilities that slow nearby enemies or make them do less damage. You can also add triggered abilities that will activate every now and then. Like maybe a knockback ability that goes can be used every 30 seconds. The only strategy should not be simply surrounding your highest DPS hero with as much buffing as possible.

Another suggestion is about the enemies themselves. I have seen some variation in speeds, quantity of enemies and hp of enemies and I like this so far, but I think it should be taken a little further. There should be the slow high hp heavy hitting enemies and the many fast ones etc. There could also be ranged enemies that don’t need to get in your face before attacking or mages that can cast spells on you from afar as well. AOE versus single target dps can counter some of these enemies and you can add crusaders that can help in other ways such as ones that silence the enemies or force them to move into melee range.

These are but a few suggestions and there are many ways to make this a more in depth experience. In its current state I don’t believe you have gone far enough to really make much of a splash. The amount of people that play and how long they play is directly proportional to the quality of the game. If you make a quality game that is different in a meaningful way you will attract many people. People do care about metacritic scores.