Before humans in NA it was a lot wetter (not because of humans obv). Fire wouldn't spread as much, just like it doesn't as much in the PNW.
False. If this would be true, then why we still have an Amazonas forest?. The empirically observed facts show that each time a lightning happens in the rainforest, its effects are short and limited. Is quickly extinguished by the humidity in soil, the rivers or by the daily five-o-clock rain.
Because not all forests are the Amazon, what about PJ forests with minimal humidity? Or the scrub oak chaparral of the California foothills?
Eucalyptus and sequoia are both fire adapted trees.