There are differences in the way Nosler Partitions and Swift A-Frames do their job, but they are more varied than you suggest, and often more subtle.
First, penetration is at least as related to frontal area of the mushroom as weight retention, which is exactly why A-Frames don't penetrate any deeper, on average, than Nosler Partitions or equal weight and diameter. This is especially true of heavier, larger-caliber Partitions, which have the partition moved forward so they'll retain more weight. Nosler designs them to retain at least 75% of their weight, even if they lose the front core, but if they do retain some core they normally retain about as much weight as A-Frames.
Second, the shape of the mushroom also has considerable effect on the wound channel. If flat or "cupped" (like a Partition that's lost its front core) damage from cavitation is increased considerably beyond the diameter of the bullet. This is why flat-nosed or cupped solids do more internal damage than round-nose solids, but also applies to expanding bullets. A-Frames end up with a rounded mushroom, which creates a hole in vital tissue almost totally due to the wide diameter of the expanded bullet. Partitions damage considerable tissue too, but more of it results from slightly more "shrapnel" and a flat/cupped mushroom.
Third, apparently the vast majority of shooters aren't aware that only the FRONT end of A-Frames is bonded. The rear end isn't, which is why the rear half often bulges widely when the bullet hits larger bones, or even softer tissue at close range. This also reduces penetration, but helps makes a bigger hole.
The jackets of Nosler Partitions are made of gilding metal, which is harder than the pure copper of A-Frames, and the jacket over the rear core is thicker as well. Consequently it's rare to see a recovered Partition with even a slight bulge in the rear core, and I have yet to find one where the rear core punched through the partition, but have seen that with the occasional A-Frame.
Both are great bullets, but the A-Frame cannot be simply termed an "improved" Partition, because of the several other differences, especially in materials and jacket thickness. Partitions work in other ways that affect both penetration and wound channel, far more than merely bonding the front core. I know this because I've tested a bunch of both in various kinds of media, including animals.
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