Although my SPG CC is my #1 and has been for yrs. If I had 75k being spent every month, no way would it ALL end up on my SPG CC.
I would spread it around with some going onto my USBank Flex card every $20k = a free tkt up to $400 (you will earn miles and EQMs on those) 30k = up to $600 and then some on a Chase CO MC. (SPG has a lousy rate 2 spg = 1 mile on UA or CO).
Just as with the stock market or any investment "Diversification" is the key and Important, no different with Miles & Points