I have to confess, I'm pretty pleased with the decisions I made with Burner.
The first substitutions were to cut the Allay and Shatterstorm for Wear/Tear. I really love those cards but they are narrow and fit better in Commander formats, where multiple artifacts or enchantments will need to be destroyed. In 1v1 games, picking the right target at the right time is usually enough.
Then I decided I needed to replace Energy Bolt. I wanted a card that would do two things: 1) Not be a creature and 2) provide me with a way to forward my win condition.
This is where I run headfirst into the problems with modern Magic designs. Creatures matter and spells are less about where it's at, unless we're talking Planeswalkers. But even the planeswalkers in the colors I am running have a very strong creature focus: Nearly every iteration of Ajani has a +1 involving creatures. Elsbeth puts creatures into play. Gideon relies on creatures (creatures I want to destroy). Koth is for a mono-red deck, Tibalt is a bit too risky and the new flavor of Sarkhan (Sarkhan Lite!) I didn't even consider. Partly because he's so new but also because he's over $30 and I'm evoking the My Money rule.
Ajani Vengeant might have a place and the Chandras...maybe.
Truth be told I didn't consider the Planeswalkers because My Money > Less of My Money. Still, if it is necessary for a deck then those things can probably be acquired in time, assuming they don't break the bank.
If I am not going to spend a lot of money then what are my options? Straight out burn spells are frequently inefficient or too small to get the job done. White wants to give me creatures. I don't want creatures, because that gives my opponents options they didn't have before. What do I do?
Then I remembered stonethorn's victory condition: Assemble the Legion. I was reluctant to add it in at first, because of the creature path to victory but I wasn't coming up with any better ideas so I thought I'd give it a test.
Against stonethorn, Burner tested admirably. I didn't win those matchups but the games were tense and the Legion presented an avenue for pressure that squeezed stonethorn against the Pyrostatic Pillar/Spellshock cards.
He took a look at the deck and wondered if I had "too much cycling". I smiled because I know that drawing cards in an uncounterable way is Good Times, especially under my win conditions. But stonethorn agreed; the deck was a solid build, it just needed something to push it a little further. I decided to up the ante: cut Cave-In and Steam Blast for another Renewed Faith and a third Assemble the Legion. Awww yeah.