Find x, where C(x) < 0x00000000FFFF0000000000000000000000000000000000000000000000000000
This requires to bruteforce 4 bytes = 32 bits ?
I believe that it is the same difficulty as a standard difficulty of 1
Seems to me this would just allow attackers to guess people's passwords and thus be able to steal wallets rather easily.
Yes... but the point is that people use strong passwords (weak passwords are weak). It is also very expensive to check passwords if the as the password strengthening function takes a bit of time to compute.