That's not a bode plot. Bode plots have logarithmic amplitude and frequency scales, so that simple filter roll offs are straight lines, e.g.

Whether that matters for your use case is a separate issue.
Apart from that, the 50ohm load doesn't appear necessary....
The sig gen's output voltage will be stated presuming a 50ohm load, i.e. a potential divider with the output resistance and load resistance. If the load is open circuit, then the voltage will be double that indicated on the sig gen.
Correctly terminated cables become important at high frequencies. "High" depends on the combination of cable length plus frequency (sine waves) or risetime (rectangular/trapezoidal waves). I doubt that is important at 200kHz.