Liquidity buffer is definitely important. The thesis of the OP is still wrong - profitability is not a sign that a broker is safe to put capital in. In fact, outsized profitability might be a red flag that the firm is selling icecream in the front and crack out the back.
No financial company wants to be in the news for stealing Bill's family farm.
The OP made his money analysing regional banks and underwriting puts against their balance sheets
FCF is what matters more than any other indicator.