I could rather easily put you in Rank 1 with that card, but I'll only give you hints because I had to discover the golden ratios on my own too.
First, AM's clog the hand and only provides speed. The goal of a firestall is not speed. Imagine having x2 draw and still only an 8-card hand. Would you want it filled with 8 AM's? No. Pack an appropriate amount IF ANY. I'll let you test how many is optimal.
Second, the difference between x2 mark and x3 mark isn't big. You'll want much more HP than you currently have and your upgrades do very little (Fahren is easily a top contender for most useless upgrade. Elixir isn't bad but Bolts do the same (and more) even unupped. Lance is economical in that it saves 2
unlike Deflag which only saves 1. However, a Tower provides Quanta for -any- card). HP gives leeway and the AI needs -tons- of it.
Third, there's a golden ratio of CC and PC in each League in the Arena. Test, experiment and test some more.