I'm not sure that is a fair statement. John Deere rates their loaders with a standard bucket which, in the case of an H180 loader, is 320 pounds. Also, look at the numbers 18 inches forward of the pivot pins. Many companies don't publish those numbers. You will see if you scrutinize the numbers that the JD 4R series has a more powerful loader than most CUTs. Then take a look at height, reach, and breakout. Then consider that most CUTs don't offer a mechanical self leveling loader as an option., Then consider the quick attach detach of the JD loader. I'm not saying that the JD loader is better straight across the board, but certainly better than most, and it can't be said that they are weaker than the rest of the industry.
Looks like JD did beef up the H180 loader weight specs over the 400x specs, though the loader lifts about 3" lower. They pretty much all use a standard bucket for the measurement... Not a whole lot of weight variations with a 72" wide hunk of metal. Here are the numbers of competing large CUT cab tractors. Note that Deere has the lowest 3pt lift of any the competition (not sure why). Also note, that the TYM, LS, Kioti & Mahindra loaders were not fully represented because they do not post lift numbers at 500mm... However the Mahindra & Kioti loaders list the highest weight lift potential at the pivot pin measurement ... FYI.
TRACTOR----LOADER MODEL---3PT LIFT @24"---LDR LFT @ 500MM----LDR LFT @ PP---LDR LFT height-----LDR LFT 59" @ PP---LDR LFT 59" @ 500mm
Massey 1758----DL130------------3084lbs---------------2056------------------2527-------------113.5"-------------2648-----------------------2299---------------------
Kubota L5740--LA854-------------2980lbs---------------1878------------------2489-------------112.3"-------------3097------------------------2509---------------------
Deere 4066R---HL180nsl---------2500lbs---------------1846------------------2486--------------109"---------------2957-----------------------2022---------------------
Deere 4066R---HL180msl--------2500lbs----------------2178------------------2477-------------109"---------------2944-----------------------2825---------------------
Kubota L6060---LA1055----------2976lbs----------------1784------------------2361-------------112.3"--------------NA-------------------------NA----------------------
Deere 4720------400x------------2500lbs----------------1742------------------2368-------------1128"--------------2701-----------------------2154---------------------
Deere 4720------400cx-----------2500bls----------------2571------------------2383-------------112.8"-------------2696-----------------------2639---------------------
Mahindra 2555---2555CL---------2945lbs----------------N/A-------------------3122-------------115.4"--------------NA--------------------------NA---------------------
Kioti NX6010-----KL6010---------3177lbs----------------N/A-------------------2761-------------108.3"--------------NA--------------------------NA---------------------
TYM T554---------TX55------------2945lbs---------------N/A-------------------2478-------------109.8"--------------NA--------------------------NA----------------------
LS XR4046--------LL4102---------2756lbs----------------N/A-------------------2500--------------96.1"--------------NA--------------------------NA---------------------