The 12 round capacity of the USP45 is a winning attribute that is still respected to this day. The only other pistols offering this kind of capacity are the Walther PPQ and the FNX45. Today, it is not uncommon for pistols in 45 to be limited to only 9 or ten round capacities. Most of this seems jto be due to them wanting to narrow down the grip to achieve better ergonomics that more shooters will find appealing.
The USP seems to have the best ergonomics in terms of having the better trigger reach that most shooters find manageable. The PPQ may have a bit of an edge over the USP on ergonomics and just flat out having better trigger reach, but the USP was ahead of its time in my opinion. The FNX45 seemed to have an unacceptable thickness that made holding it more of a chore than anything. The fat grip of pistols chambered in 45 can be one of the deciding factors for people looking at using a 45 caliber pistol. I know that for me, the USP is still the top pistol as far as ergonomics and trigger reach, except for the PPQ, which is striker fired and therefore not much of a valid comparison.
In other pistol designs, the recoil springs work to slow down the slide throughout the travel of the rearward movement. After the full length has been traveled, it is expected that the frame of the pistol can withstand the remaining force of the slide pushing rearward.
The design of the other H&K pistols seem to have left this double spring system behind in favor of a heavy flatwire spring and a nylon buffer to act as a sacrificial piece to absorb the force of the slide coming to the rear. The system seems to work in providing longevity and slight recoil reduction on the 9mm, but I feel like the .45 and .40 get a bit more recoil with this system. Perhaps H&K are compromising to save some dough?