While you can see resemblances I don't, it still doesn't change the fact that this comparison is a far stretch and is so unlikely that it almost definitely isn't true, especially when looking at Gardevoir's prevos. (no offense, if that sounded harsh). :P
Bulbapdedia may not have a source, but at least they have a good explanation and can trace parts of the design to the culture where the game is made (which isn't always the case, but oftentimes is).
Also, not to mention all of the name translations and other aspects for Gardevoir and it's prevos don't mention anything catlike, unless dancing, sensing emotions, using psychic powers, and protecting someone are things that only cats can accomplish. Also, the prevos (and Gallade) don't really have the catlike resemblances your mentioned, and it isn't often that Pokemon would randomly add a resemblance in a evolution unless it made sense. :P
I'm almost sure the designer gave Gardevoir the 'horns' and 'whiskers' because it looks like either eyelashes or a traditional mask you'd wear while dancing. The big red horn probably comes from the Red horns on the prevos doing stuff with emotions, and now it is on the heart because... emotions. :P
I'm just saying that it is immensely unlikely that Gardevoir takes any inspiration from any cat of any kind, so while you may believe Gardevoir looks like a Maine Coon cat, that doesn't mean it took any inspiration from it. Just because 2 things look a tiny bit similar in a few ways doesn't mean one was based off of the other.
Because you cannot draw any comparison other than those subtle coincidences (which are not widely agreed upon, as well as some being a stretch), you can't make a case that has any more grounds than a wild guess, whereas bulbapedia has a respectable amount of evidence that suggests Gardevoir is based off of a dancer and a protective person. :P