After reading how you contrast Charizard and Litten, I'm a bit more on board with the fire/ground type.
Curious though - how familiar are you with kanji? The extra extension of the lower end of center line actually makes a word of a difference, and would be an entirely different kanji.
In fact, I kind of assumed that as Litten evolved, the dashes on his forehead would slowly change to the "king" character.
It's actually a bit of a cliche in many animes to have the king character on the forehead of a tiger character, as it matches us nicely with how a tiger's stripes are often depicted.
Unfortunately, I'm not too familar with Kanji myself, so yeah, its possible the stripes on Litten's forehead may be something different and may become the King character. Luckily, my theory is more based around the Tiger and Dragon relationship as how they're depicted in Chinese tales. If the stripes are indeed the Kanji for Earth, or King as you say, its only a nice throwback and may or may not support the Fire/Ground typing idea further.
In fact, my theory isn't just about the Tiger and Dragon, but I was one of the first to support and suggest a Rock or Ground typing for Litten's evos. Somewhere in this thread I have a extensive theory written up that may hint to the Ground typing further. I also suggested the Ground or Rock type for Litten mainly because it would edge nicely with the other two starters forming the three layers of nature:
Litten's Evos - Fire/Ground - Land
Rowlet's Evos - Grass/Flying - Sky (In the chinese elements, the element of Wood includes air in its definition)
Popplio's Evos - Water/? - Sea