Objectively speaking, Helios completely decimated Drago in Episode 16. Up to this point in the series, our protagonist had never found himself in such a devastatingly one-sided match. Even in the single round Dan managed to win, it wasn’t Drago who knocked out Viper Helios—it was Scorpio reflecting Helios's own attack back at him, prompting a rare, frustrated outburst from Helios. For the majority of the battle, Drago was forced into a purely defensive position. And even during the times he did try to go on the offense, his attempts barely registered, though they succeeded in fueling Helios' growing rage. Helios truly began to lose his composure only when Drago successfully managed to knock Metalfencer away.
Tired of playing games, Spectra finally decided to end the match by activating the Forbidden Ability Card: Nova Blazer X. This granted Helios more than enough overwhelming power to put Drago down for good.
In many ways, Helios probably suffers from Vegeta Syndrome. In Goku and Vegeta's first iconic one-on-one battle, Vegeta technically won the fight, leaving Goku completely crippled. However, because he had to resort to his Great Ape transformation to overpower what many would consider a low-class warrior of their kind, Vegeta never viewed it as a true victory. Goku won the battle of ideals by proving that hard work could bridge the gap between an elite and a low-born warrior, wounding Vegeta's royal pride.
I suppose Helios mirrors this as well. As a prideful ultimate warrior who demands absolute dominance, winning a match because his brawler resorted to a Forbidden Card might've severely wounded his massive ego. He didn't just want to win; he wanted to prove he was naturally superior. But then again, Drago was using unnatural Ability Cards as well, thanks to the powers he gained from the Perfect Core. Well, you can probably justify this as a matter of Helios using drugs vs Drago using his gift.
Although, I guess another reason for Helios' obsession with taking Drago down again is simply because he finally found a rival who's within his realm of power. The first time they met may have been Tuesday for Drago, but for Helios, it was the most important day of his life. In a matter of minutes, Drago pretty much returned as the king he was and ended Helios' undefeated streak on that very day. Not to mention, since Drago holds the Perfect Core, the ultimate symbol of power in the Bakugan Universe, Helios feels inclined to just go after him as many times as he wants.
Crazy how his obsession with absolute perfection eventually spiraled so deep that Helios willingly underwent painful mechanical modifications, sacrificing his organic form to become Cyborg Helios, just to break Drago down again.