As it is shown in practically all comics, supervillians are products of
the heros who fight them.  How id metropolis or Gotham survive before
Superman or Batman came along.

Or it could be that somewhere in the past, the SWAT Kats ancestor (or look
alike, or on what Ryan would say, TWINS!) once fight a group of villains
just like the ones in the present, and now at the present, the villains are
back, and so are the SWAT Kats.

Note the eps, practically all of the SV in SwatKats were created through
the intervention of the SKs themselves.

Almost, Dark Kat caused the SWAT Kats to exist.

Of course, when they are planning to make the series, they make some
villains so that the SWAT Kats won't be left alone just only to fight
termites.

I think that The Ghost Pilot and Madkat were supposed to be a recurring
villains.

Bigger question: are there other superheros in MKC besides the Swatkats?

No, unless that episode want to have another one. Or maybe there is one in
someone's fanfic story.

Even Bigger question: would alt.fan.swatkats accpet parodies?

alt.fan.swatkats who?

I was thinking of the "TwitKat!"  (with Bonehead, Loser, Dep mayor Callus
Brat, chief Ferrett, Mayor Stanx, reporter Aye Beggora, and the
supervillian: "the Message Poster".

How about Barnes and Felicia Farrel?

BTW, "The Postmaster Always Post Twice"?

(excuse that last part, just thinking out loud)

Good, since that if you do really mean it, I brat you from here to Megakat City.