As I once state din another thread, the main issue that some CLAIM to have with cross training is the whole silliness of "jack of all trades, master of none".
The reality is that has ZERO to do with it because the TRADE is fighting.
Let me say it again, the TRADE of MA is FIGHTING.
For a MA that is a striker to training in a different MA ( perhaps grappling) to perfect his fighting skill is comparable to a welder that is proficient in TIG welding training in MIG to be a better welder.
The trade is welding, the cross training is in different TYPES of welding.
The trade we do is fighting and the cross training is in different TYPES of fighting.
When we cross training in the aspects that are not prioritized in out base MA (like grappling is not prioritized in WC for example) we are MASTERING our trade (fighting) because we are become proficient in ALL aspects of our trade.
No one is a master welder if he only knows ONE method of welding.
No one is a master MA if he knows only ONE aspect of the MA.
To cross train is to become a master in the trade that is Martial Arts.
Psalms 144:1
Praise be my Lord my Rock,
He trains my hands for war, my fingers for battle !