I there any point to use BOMT (if you have a choice oc) instead of Sword of Miracles for a mystic. Both have same math. SOM has better atk and most importantly: both have acumen SA beside the fact you can use a shield with the sword.
The SOM is popular precisely because you can equip a shield. Mages would rather reduce their evasion and have a chance to block attacks with the shield, than to have no shield at all.
The SOM is also a "fast" attack speed weapon as opposed to the "normal" attack speed of the BOMT. It's not often that a mage will find themselves needing to use a melee attack, but if you do, your options are to swing faster and do less damage or swing slower and do more damage. Again, not a major consideration for a mage, but maybe something that an SK or an Orc might consider.
If you don't PVP, get a BOMT. The prices of BOMT's on Devianne are usually around 60M. The prices for SOM's are around 80M. You can craft both for much less, of course, if you get lucky with the 60% craft.