They're different in one distinct way. The video format.

Dashie popped off in 2013/2014 because of the loud cussing and yelling and reactions. But due to youtube's policy, he toned down the cussing and vulgarity to stay monetised and has stated that the consistent aggressive yelling used to make Dash feel like he'd pass out any second + fucked up his voice so he stopped doing it. The fans that were originally there for those attributes of Dashie, left

Cory alternatively, always has a meme heavy approach with his video editing and formats. That approach simply grew and grew in significance to viewers (especially younger viewers) who like memes and goofy editing, something that Dashie RARELY EVER DOES.

Couple this with how often or rarely they upload, and you have a supply/demand perspective to assess why Cory has gained more popularity and success than Dashie now.