do we know anything about Shi Huolong's martial arts level, other than that: 1) he crippled himself while learning the 18 Dragon Palms, resulting in the mastery of only 12 palms, and 2) after some palm clashes with Cheng Kun, both parties were injured?
Like someone else pointed out, I think he must be very good to do (minor) damage to Cheng Kun. Actually he might be as powerful as the Wudang heroes and the Ming Cult lords. But I would guess he is sometimes ranked lower because of Yelu Qi. Yelu Qi is supposed to have mastered XL18Z, and yet during his heydays he couldn't even beat Huo Du. So some people may think that Shi Huolong should be weaker than Yelu Qi because Shi only learned 12 palms.