I think it's a false assumption that when something burns in a high severity fire, it returns to a healthy state afterwards. Historically, natural fire was low severity because it was high frequency, burning through once a decade (or even more frequently). This left large trees and soil intact, and so dense regrowth was limited, since there was still shade.

With high severity fire, two things can happen. Trees can be totally wiped out (called a stand-replacing fire) which causes extremely dense, brushy regrowth (prone to another high severity fire). Or in really bad conditions, the soil can be damage so no regrowth happens, causing strange moonscape-like forests that are completely dead. This affects watersheds, causes mudslides, etc. Neither is good.

If we could burn large swaths of landscape with low severity fire, that would be a huge step in the right direction but is extremely difficult. We are treating only a small fraction of the acreage in that manner.

Note: This varies from landscape to landscape but is directionally correct. For example, in some climates, stand-replacing fires are healthy and normal. But in most climates, bad.