I fully agree with comment 91, bad design.
But, then again, I am no engineer.
So, was the person that designed it an engineer? or.....
So two people who aren't engineers think it's a bad design. I'm not going to provide my resume but I don't think it's a bad design, just poor execution i.e. due to poor welds. You could try to make the argument that a good design would be immune to poor execution but we live in the real world.
Notice as the capacity of loaders increase, there's an increase in complexity. I have an LA1065 loader on the MX and an LA1154 loader on the M6060. Both loaders have the cross tube piercing the loader arms. Obviously this results in twice the weld length to resist torsion of the tube compared to the non-pierced arrangement on your loader.
Now look at the loader on the L47TLB that my friend bought yesterday. It's rated at 1,300kg so more than the MX and M, and notice how the cross tube pierces the loader arms, but also there's a cap that plugs the end of the tube. This systems offers close to three times the weld length for torsion, but also reduces the chance of the tube collapsing (buckling) under load.
The Japanese put a lot of thought into their products and the loaders are no exception. You can bet that the loaders on all models are designed by engineers, and that software tools such as ANSYS (finite element analysis) are used along with extensive empirical testing.