Core-Lokt are not cup and core. Gen1 were originally mechanically locked bullets (like partitions), and had a reputation for failing (as noted in many magazines of the day), but less so than cup and core of the day. As did most bullets from the "Era of Rotten Bullets". Core-Lokt were considered premium bullets (and are now bonded).
Rifles from the rotten bullet era also had more modest velocities (outside of Weatherby), and stories of bullet failure were still common.
Rifles now run much higher performance windows (even 100 yr old cartridges with new powders), and bullets are made much better. Doesn't mean a 100 yr old rifle cartridge and 100 yr old bullet design can't work, it just means technology has improved reliability.
I dunno that original Remington Core-Lokt bullets were ever in the same league as Nosler Partition bullets.
However, I do agree with you that the original Core-Lokt bullets were never the best choice for what I consider unnecessarily high Weatherby velocities, in any caliber.
Also, I don’t care for ultra-velocity cartridges, (“bah humbug” LoL), except for hunting rodents at long range with small bore cartridges.
At original .30-06 velocity I have, beginning around circa 1967, used 150, 180 and 220 gr .30 caliber Remington Core-Lokt bullets and experienced nothing but perfect success / 100% reliability, both in N. America (Nevada, Idaho, Alaska and Soviet Occupied California) plus Africa as well.
Likewise I’ve enjoyed the same 100% success with the old fashioned Hornady RNSP and their original Spire Point bullets both.
Here in Alaska, where I have lived for a tic over 41 years now, I’ve also experienced the same 100% reliability with the .375 H&H and both 270 gr and 300 gr RNSP, Core-Lokt Remington factory loaded ammunition (again the old fashioned, original Hornady RNSP as well).
Many USA hunters tend to waste way too much time and thought into reaching for extra high velocity for shooting hooved game.
I always recommend heavy for caliber, round nose soft point bullets, with plenty of lead showing at the tip, fired at “normal” velocities, for “normal” hunting ranges (out to only about 300 paces or so.
That said, my favorite premium bonded soft point is the Swift A-Frame.
These indeed work well for old timey cartridges, such as the .30-06.
And, they also hold together well even with the higher velocity cartridges, such as the Weatherby designed ones too.