> The study didn't account for the growth of new vegetation in fire-swept areas
That's a pretty important caveat. In a steady state, forests fix some carbon, but dead leaves and wood also release carbon (and methane, which is worse) into the atmosphere as they rot. On the other hand, charcoal, once buried under new growth, is actually a really good way to sequester carbon. And recently burned areas are going to see very rapid vegetation growth, which will fix carbon. So yeah, over time scales of a few years, forest fires release lots of carbon, but over multi-decade timescales I suspect that a forest that gets periodic alternating cycles of fires and regrowth is going to sequester more carbon than one which doesn't. Especially if those are relatively cool fires which burn the undergrowth (which grows back very quickly) but leaves the big, mature fire-adapted trees behind.
That said, while many of these ecosystems are adapted for fire, they're adapted for the less intense fires you get when they're caused by lightning that is usually accompanied by rain (last year's Big Basin fire being a freak exception). In recent years, most of the wildfires in California were caused by human ignition sources, on hot, dry, windy days, when the fires spread faster and burn hotter. So instead of mostly just burning undergrowth and leaving the older trees behind, it burns everything. That's harder to recover from.