I keep 100k in an IRA at Merrill and get 2.625c cash back; it is simple - even when I pay state taxes, I get a float and a small rebate.

But before we get worried with the changes, look at the numbers.
Platinum Honors 2.625-2.25 = 0.375% difference
Preferred Plus 2.25-1.875 = 0.375% = same drop

On $1M spend, (not too many do above that I hope) the difference is $26250 vs $22500 = $3750
For 100k in non-bonus spend each year = typical = 375$ – not much to worry about

Real options are
A
Flexible currencies
Citi or Cap 1 with transferable points @ 2c each vs 2.25c below
B current
IRA 100k at BofA with 2.25% Preferred rebate
= $22500 per Million spend = $2500 extra cash vs (20k cash /2M points)
or
for typical 100k spend each year = $250 cash loss (2250-2000) vs having option of $2000 / 200k points
C
Business at 100k Savings Account = 3% interest – itself has lost cash or investment opportunity
– Unlike an IRA, this account will have a real cost – say 3% in return = 3000 a year
even with a business 1M spend = gain of $3750 and loss of 3000 – really not worth it.

Between B & C, B wins for simplicity
Between A & B – I suspect that depends on your balances in Citi and Capital One
I will likely change my Venture X to a Cash Plus 2% card for flexibility or look more closely at Bilt

For typical 100k spend each year – just get SUB from every card slowly and steadily
= 5k spend for 50k points times 20 gives 1M points for 100k spend = ~ 10% SUB rebate

The 1M spenders need to up their game with BofA - move your company 401k?