Unlike other heroes in Dota 2, Dragon Knight was considered to be preeminent before patch 7.38b release, and Valve decided to change the current Dota 2 meta by Dragon Knight being heavily nerfed physically.

This can be seen by his plummet in performance as evidenced by the data from DotaBuff.

In terms of statistics, the gameplay update was released a few hours ago, and he has already lost 4% of his current win rate. He is also losing more than half of all matchups currently sitting at below 50% which is approximately 49.53%.

The reason for that loss is attributed towards the downturn in performance due to the implemented nerfs in patch 7.38b. The Fire Dragon aspect of the character was severely shattered as his damage and the radius of both AoE abilities were slugged.

The alterations Are outlined in the following :
Dragon Tail- in dragon form the lofted radius of the squeeze is revised from 175 to 100.

Wyrm’s Wrath- The magic damage was reviewed from 10/20/30/40 to 6/12/18/24.

Don't forget that a new meta was implemented in Dota 2 and now the most powerful characters are starting to dominate.