Yes I totally agree. So in that sense it's good that the fantastical creatures will be rare in Elemental. But it's definately possible to keep a dragon rare and powerful also in a world with say orcs and goblins. If you had entire armies of dragons (like in Silmarillion, earlier referred to as a main inspiration for Elemental by the way) then you would need to add something else which is rare and even more powerful, like a demigod or the like. It's all about inflation and relativity.
But that's the point. If you add in hordes of goblins and orcs and elves, they stop being something exciting. There's almost no point in adding them in because they just sort of fade out into being regular run of the mill units and you don't pay a second moment's notice to them. Having all fantastical creatures (besides the Fallen, of course) being on the rarer side of things makes the fantastical element of the game that much more exciting and fun.
To break cliches just because they are cliches is very bad. To break them to offer some really interesting and with sense, is another thing. If Stardock could do the second, then ok. If not, let Unicorns alone. (doesn't D&D already have en evil unicorn?)
Regarding the clichéss I think it has to be remembered that there is a reason for something being a cliche. Some images and concepts resound strongly within people in a certain way, that's why they become so popular that they eventually turn into clichés. The difficult thing is to be creative and come up with something new that still resounds as strongly (in a positive way!) within people. If Stardock could do this it would of course be the best. But I must say that often in books the author fails terribly in trying. They try to be fresh and modern and end up with something that just feels contrived or worse. And in games it's often even worse since so much effort goes down on the technical side and other aspects than the story/world concepts. So please, no "fresh" evil unicorns or vampires choosing their alignment freely.
Of course, but with some creativity it is possible to get away with butchering clichés and even to be better off for it. And, have you ever read the Coldfire Trilogy by C.S. Friedman? They're great books, and one of the protagonists is an unlikely vampire-like antihero, and she made it work very well. It doesn't take creativity to say "this is an evil unicorn LOL!" But it takes creativity to ignore such an ingrained cliché in a meaningful way that actually convinces people - and it is very possible to do so. And one thing to consider is that many such clichés are not at all explained. There is rarely any reason given for why unicorns are such good and pure beings, and unicorns are usually considered to all be such heavenly beings with no exceptions - no rogues, no variance. So if you provide a good reason or background to support an unconventional choice, I think most people will be more than happy to accept it.
I think if you said, for example, that Unicorns in Elemental are self-interested beings (maybe even especially so since the cataclysm) inherently connected to Life magic, you could make them much more interesting. Their greatest powers could still be healing and all, and maybe they'd still lean towards the good side of things, but if they would benefit greatly from siding with an evil power they wouldn't be fundamentally, irrevocably opposed to doing so at great cost. Frankly I think that's a much more interesting take on things than "unicorns are shiny, good and pure beings that chase away evil." The latter honestly is a little demeaning in my opinion - it basically makes all unicorns the same, it removes their independence and makes them purely instinctual, and also makes them too perfect - why can't unicorns make poor decisions like anyone else?