If this were my goal I’d start with any escaped wichurana rambler I could collect a runner from. Roses like Dorothy Perkins, Excelsa, Turner’s Crimson, Hiawatha, Minnehaha, American Pillar, etc. They were really popular at the turn of the century on homesites and as living fences for railyards and farmland.
You’d need to breed out the affinity for mildew, but these ramblers have thrived despite all of the neglect, eradication efforts, and the introduction of invasives, pests, and diseases. They’d be sure to put out some monster seedlings, but also have a place in any breeding program in search of drought and disease resistance.
Like this monster Dorothy Perkins (presumed) rose growing wild near a lake in Oklahoma:
Source
Note: if you’re in an RRV heavy area you’ll need to develop a quarantine/eradication protocol for eriophyid mites before introducing to your garden.