I dont understand

So basically i went through sh*t until my blade dancer got to level 13 ( the cards was easy but the orbs that took much of my time )

when i got the orbs i had 2 choices : 1- upgrade BD to level 13 and unlock a new talent and making a new unit stronger

2- upgrade cultist to level 14 ( he's my main ) And at his current level ( 13 ) i achieved >800 damage and i won that round so hes not just my main hes the most powerfull unit in my account

So of course i choose the 1st option just because i didn't want to play all my games with cultist even if i won most of them it wouldn't be fun bcz every game is the same so i upgraded my BD

So my question is why this is the best that i could get from her ? Is she that week ? Did i took a wrong decision when i upgraded her over the cultist ? Or what bcz I'm really confused