Looks like you started battle before L8, that's why I lost that attempt.
Now it's done, I guess it's good to mention on wiki, that you need level up for Avatar fight.
And some luck, sure... Sometimes all of them got ~150 damage, but may be it's supposed to be so... I used all I got and that was just enough.

Looks like I completed this game!

All challenges, puzzles, dungeons and Triple Quests are done. Miss two achievments, Boy Scout and Masochist.
And may be the biggest challenge is to beat your streak, but I'm not so crazy.

And I'm bad with these things you know which requiring
daily approach... Just have no patience. I can play for days if I need to complete VGT for example, but just play every day to have streak - no.
And BTW, VGT is all - just technicality, as you said.

Once you mastered all the classes and game itself... I do love the game and VGT in particular, the only annoying part was that scumming for GG (mostly), and sometimes for items or GETINDARE. But some classes I did easily in one try (Berserker, Warlord, Priest, Bloodmage - hard to do floors, easisest boss fight thanks to Sanguine), just when got all I needed at once.
It was a wonderful time!

This game is really so good.
I wanted to start a new kingdom and make a thread about playing it, from scratch to 100% completion, which I already did. Would not it be too arrogant? Or would be interesting? May be I need some rest now, but lately.
Many thanks to the creators!