Aperture can make seeing some things easier though. Its like everyone has their own display settings preferences on TV sets, devices etc.
Hopefully no one doubts the value of increased aperture in showing more planetary detail. Fine scale contrast transfer depends on aperture, image brightness and resolution are also functions of aperture. With aperture, comes a variety of liabilities.
If I compare the planetary detail I see in my 102 inch apo, 120 mm ED, my 10 inch and 13.1 inch reflectors, it directly corresponds to the aperture. Granted I live very the coast in the south west corner of the continental US in a very mild climate that's normally south of the jet streams..
Regardless, "serious planetary observing" can be done with all four scopes just as casual planetary observing can be done with all four scopes. In my mind, "serious observing" is an attitude on the part of the observer, a dedication to patience and perseverance.. it's really about being the best observer one can be, regardless of one's equipment.
If a 4 inch is not sufficient for serious observing of the planets, what is enough? A 6 inch is only somewhat better. A 10 inch is only somewhat better than that...
There's enough to see in a 4 inch to keep one busy...