Did you factor in Western Union's fee? If varies from country to country. For the US, transferring under US$500, the fee is more than 5%, then 5% up to 1500. It's substantial.It may depend on your nationality or where you currently reside. I am neither from the USA nor other "privileged" nations.
But yes, I did explicitly check the MG rate against WU before I replied to the OP. So it is clearly not the same for everyone.
P.S. Having re-checked rates again now, I am seeing 1214 on MG, and WU's rate is still better @ 1289. One of the things that affects WU's final rate hugely is whether you send to bank account or to a branch for cash pickup; I am not sure if the same applies to MG.