in the 1980s Joan Hagar commented to me when we worked on the Young Stand Study that the Hermit Warbler is "Our Warbler". It is abundant as a nesting bird in our coast range and the Cascades in low/mid to high elevations where it might compete with Yellow-rumped Warblers and Townsend's Warblers.
In my opinion interspecific competition is over rated as a driver for change. It is possible to find TOWA above 3000 or more feet in the west slope Cascades. and almost never in the coast range as a nesting species. I knew the landbirds in those ranges in the middle north part of Oregon as well as anyone from one to four decades ago. If TOWA has since gotten an upper hand over HEWA in that time period I would be surprised