You mean a combatant in the sense of a melee mage? I suppose the immortal heroes could pull it off, they wont rout in their own dominion -- but why would you want that? My Tien super-duper mages kick much more butt casting spells than karate-chopping with a wraith sword....
Almost all TC mages' fighting skills aren't very good, which is either too bad or a good thing, depending on your point of view. If their attack and defense were in the 10-12 range, I'd indeed be very tempted to turn them into self-buffing SC's, since they're both sacred and able to cast good buff spells on themselves. Quickness + Fire/Water blessing plus ethereal, mirror image, various shields, etc... can get pretty scary.
It might make a good extra theme for TC, though. For a nation derived from a martial-arts-oriented culture, TC doesn't have many very skilled fighters.
Tien Chi mages don't know martial arts, hence the weakness in melee. In fact, I think Lu Tung Pin is probably the only Spring and Autumn commander resembling anything close to a martial artist.
Have you ever seen any of the Chinese made movies where the different gods and super heroes duke it out using their super powers? I'm thinking along those lines. Not exactly martial arts, but it would be fun to be able to have a team of commanders decked out with powerful weapons and spells, roaming around defeating evil.
Yeah, Merry, my parents live off those movies/soaps. But not all Chinese people can kill you in four different ways with their pinky toe alone... Even though I rather like that stereotype...
Anyways, tinkthank is right, Celestial Masters are best off sniping like a coward.