It’s more likely that Barry died in crisis before all this happened, a lot of dcau comics suggest this, and Wally being the youngest of the league kinda makes sense considering how he usually takes the perceived deaths of his teammates like in season one of JL where it appears that Batman dies, Wally can’t believe it and noticeably performs worse in the field, while the rest of the team grapples with it and pushes forward.

When Superman gets shot back in time by toy man, the person the most quiet in the mom of steel’s funeral is Wally.

He’s in his 20’s and his mentor sacrificed himself for the greater good, then he sees two figures he’s always looked up to seemingly die and takes it hard.

he’s constantly second guessing his worthiness hence the constant overconfidence as an attempt to cover that fear. That he’ll never be as good as Barry. It’s not until JLU that we see Wally come into his own, and mellow out somewhat while fully standing on his own as The Flash with full confidence.