Nothing about the 25 Creedmoor is meant to replace older 25 cal rifles, but as with a lot of other rounds it's the packaging of new rifles and ammunition twisted and cut for better bullets.
So the question isn't "is the 25 CM better than my 250AI" it's "how do we make use of these great new bullets"
Whether or not heavy 25 caliber bullets better suit your needs than the older 120 grain or lighter bullets is another question.
I've been messing with fast twist 25 cal for years, like a lot of other wildcatters. The 25-06 is a beast when set up for these 130+ grain bullets. The 25 CM is as identical as it comes to the old 250AI, a sweet spot for 130 grain bullets when taking into account action length, barrel life, and performance. The 250 AI has always been a great round though, so you can't dump on the 25 Creedmoor without dumping equally on the 250AI.
Should you throw out your old 257 Roberts? I haven't, but if I have an interest or a need to use 130+ grain bullets I'll have to spring for a new barrel at least.
I enjoy and shoot them all: 257 Roberts, 250, 250AI, 25 CM, 25-06, 25 Bullberry, 25 TCU. Some of those are 1:7 or 1:7.5 rather than the old 1:10 twist. Some are pistols, like the 250AI, Bullberry, and TCU. They're all great rounds in their given roles and platforms.
This is a good move by Hornady, but I'll keep loading Bergers because I think they're better bullets.