User blog comment:B214/Shin DxD 1 discussion/@comment-93.132.65.47-20180926201139/@comment-108.7.146.103-20180927014739

Crom is far more than a "Rock Lee" He is not an ordinary dragon, he is the strongest Legendary Evil Dragon, who has constantly trained the basic Dragon abilities to surpass those of Albion and Ddraig. Not only that, but he was able to, through his own power, match the abilities of the Dragon Diefication/Maofication which combines the powers of Ddraig/Albion with those of Ophis. Through sheer training he was able to gain a resistance to Dragon-Slayers, with Isseis boosted Ascalon Dragon Shot being the only thing to damage him visibly, even the purpose built bullet that had slain Balor, (Crom's superior god), was ineffective against him. The only advantages that The Heavenly Dragons will have is their special abilities, and even then, that isn't likely to be a game changer. Not to mention their draconic pride would prevent them from using such 'dirty' methods. Have Ddraig and Albion advanced with their hosts? Yes, but not as Dragons in and of themselves. This is like Gohan in the beginning of the Buu saga, he lost the ability to reach SS-2 and was caught up to by Vegeta. Except that while Gohan did so because he's a pacifist, The Heavenly Dragons were physically sealed (until recently).

PS Rock Lee was never that good in comparison to Naruto or Sasuke, who surpassed him in physical parameters as well as distanced attacks, (literal moon busters).