20 is pretty big ie 500 Hz at 16 ohms.

The bypass cap does not 'regain' highs. It essentially is an EQ circuit, the result is to lower the mids relatively. The cap conducts across the resistor at higher frequencies. You can't consider components like that- you must view the whole circuit.

There are a few who advocate 6 db/octave, bear in mind it lowers power handling.

But best is still active crossovers and separate amps. Just my 2 cents.