One strategy is to put your "tank healer" in the second place. So, as they take damage (and hopefully survive) they get healed. Your 'Divine Healer' is perfect for this.

Then third and fourth spots (if the match has the mana allowance for it) could be characters that have sneak or magic. It's a double combo.
Feral Spirit has sneak, so does Elven Cutthroat.

Congrats on getting to 1700 ranking. That number will drop when the tournament ends in 2 days, it's just their way of keeping things fairer, but you can always get it back again.

I got the gold league twice, but I am back in the silver league again.
It's not easy. Keep going.