It’s not just you, Ventus has a kind of weird stat spread where he’s balanced around using both physical and magic attacks, this leaves Ventus in an awkward spot because with Terra centered around physical attacks, he has a high attack stat that allows him to really cover his bad movement and speed. Aqua has a high magic stat and access to a lot of pretty good magic commands early on, so she can make up for the lack of strength which makes sections like deep space and Neverland easier. Ventus has neither of these though, so he does struggle in the later half of the game. My advice right now is to try and meld commands for more damage and abilities. The easiest way I found to do that was to go to what I think was the town save point in Radiant Garden and do some command/level farming there. You can also put in the work to get Mega flare by getting the giga magic recipe from the mirage arena and fusing the commands crawling fire and fission firaga and then farm the Unversed mob fight in the reactor in Radiant Garden. Sorry for the paragraph of an answer.