If disease-resistance is a focus (and it probably should be imho) you may want to focus on newer cultivars and/or species in your breeding stock. Historically, breeders focused on others aspects, and left the issues of disease-control to a blossoming chemical industry.
I don’t know the actual history of… I’ma say… “environmental enlightenment” in the industry, but, if folks were starting to look towards developing more resistant roses towards the end of the 1900’s, the wildly successful Knockout rose probably put an exclamation mark behind that goal.
As a house that had established a reputation for some healthy plants, Kordes was probably one of the first breeding houses to seriously commit to resistance as a primary goal and, reportedly, had a real wake-up when they decided to go entirely no-spray. After making that commitment, they feared for their entire stock of plants as they watched and saw the extent of the disease pressures in their fields, and the chemical dependencies of their stock.
Generally though, introduction by Kordes post-2000 have very good resistance. But their earlier of the newer introductions mostly lacked fragrance. Many had other deficits as well, and the more tolerant plants would often be deemed too prodigious or not quick enough to dedicate their energy to blooming for the impatient gardener.
They are becoming more committed to the other aspects as their “Parfuma” and “Nectar Garden" collections attest. The French breeding houses probably maintained a less singular focus and their recent offerings also have improved disease resistance with quite luscious blooms.
Realistically we need to realize that no matter the phenotype (part of their genetics that are expressed and evident to us) of any parent, the genotype is much, much, deeper, and carries a lot of baggage in the genetics of the inferior ancestors. For example, Kordes, as I understand it, germinates hundreds of thousands of seedlings each year. The percentage that make it through their trials to get to market is abysmally small. It is metaphorically the roll of hundreds of die that come together in any one seedling that is ultimately deemed “marketable" but thousands of siblings were culled in the process. The odds of any one offspring, in turn, of that seedling sharing all of its best attributes is next to nil.
There are many healthy and Fragrant roses out there now. The vast majority are pink. Obtaining a trifecta of health, recurrence and fragrance in e.g. a deep red or saturated yellow is essentially a holy grail of the hybridizer.
(Take my assertions with a grain of salt! Others no doubt have a deeper understanding than my generalizations, and corrections nay be in order.)