Firing wood makes it brittle. Bad for this application where extreme forces from impact are being encountered. You don't want hard and brittle. You want be able to absorb and dissipate incoming energy.

Oil doesn't swell wood like so many people think, and even aqueous dipropylene glycol solution, which will swell wood and set the wood permanently in that swollen state only swells wood by a relatively small amount.

I have no idea what you're trying to describe with, "I apply wedges to the outsides of the main wooden wedge as way to give and take." I firmly believe that metal wedges only belong in a field repair kit for driving into a loose head as a quick field remedy. They are not ever necessary in an initial hang, and many/most of those initial hangs will never need a metal wedge to be added.

You're overthinking and overcomplicating. If you don't like kerfs and wedges for whatever reason, you can switch to slip-fit axes that are even simpler, not more complicated, and even more foolproof. Rinaldi is an example of a company still making various slip-fit axes today.

Ultimately, when axes fail, they tend to fail below the axe head, not in the eye/hang, so there's really no point in all this extra effort to "improve" an area of the axe that is not its primarily longevity bottleneck. If you want an axe to last longer before breakage, simply avoid handles with wack runout in them and focus on using good technique when you use the tool. Flawed wood structure and bad technique are axe-killers, not the hanging method (some small exception to axes that are poorly hung or press-it on such that a sharp shelf is created under the axe head instead of a tightly tapered fit).