I understand perfectly the reasons of this system, and as you say, B standards can be modified.
I just find surprising to have qualifications for 4x4, 5x5 bld and multi. I hope that we will see a non-empty final of 5x5 bld !
Also, some A/B Standards are stange, but I think it's regarding the US level. I think everyone can have a sub-30 average of clock in about 30 minutes of practice, but getting a sub-40 average of square-1 is much more difficult !
In general, I think that for side events, Magic, Pyraminx and Clock A/B Standards are easy, and that Square-1, 6x6, 7x7, 4x4 and 5x5 are hard.
... and I saw that the 4x4 A/B Standards have been modified, but not the 5x5, so under 30 minutes for 4x4, but 20 minutes for the 5x5