Yeah to my understanding, the Delaware was THE meat bird before the Cornish X, but once the CX came on the scene, the Delaware started to be bred more for egg-laying qualities. So your typical hatchery Delaware today will be more of a layer and less meaty. I think McMurray is trying to replicate...
I haven't raised these myself but wanted to post this since you memtioned Delawares:
https://www.mcmurrayhatchery.com/delaware-broiler.html
Egg lays and bred to be meaty