Expectation is one thing, but Derrick White going MIA all season long is another.
And DWhite has been with the team since 2022. What gives with the sudden drop off? He looks as bad or worse than his 2022 slowly-developing form.
I took a closer look at Derrick White's metrics to see if there was anything there to explain things. Here are his splits from Basketball-Reference - the ones I highlighted are his +/- in wins vs losses and his April performance (playoffs) vs regular season.
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This confirms what I've felt for a while - Derrick White's value is in the fact that he's a force multiplier. He makes other players around him better but he can't carry a team when its stars are not playing well. He is a +21 in wins and a -7 in losses. That's why I always felt expecting him to be a No2 option is unrealistic - his shooting is inconsistent and he can't really create his own shot. But he can come off screens or off flare actions and shoot, or he can drive and kick the ball, and obviously all the other things like rebounds and defense, like his rebound that led to the Tatum 3 that led to the win in G3.
But the data also shows while his ppg has dropped to 10.3 in April, and while his FG% is actually better in April than it was in March (47% x 39%) his usage has dropped off. It's gone from 22% to 12%. He's just not shooting the ball as much, or they're not running actions that end with him taking a shot. His +/- is still high at 25 which is probably beacuse of the two 30-point wins.
Then I looked at his percentiles from Cleaning the Glass, and that Usage number is supported by their data too. Here is his usage in the regular season and in the playoffs. In the regular season he was in the 70th %ile (top 30%) for combo guards in usage, and in the 86th %ile in turnovers committed (that's basically top 14% of players in terms of taking care of the ball). His PSA (Points Per Shot Attempt) was in the bottom 35%, an indicator of his poor eFG%.
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Then you look at the playoffs. His usage has dropped to the bottom 18% of combo guards in the playoffs, and his turnover rate is has dropped to the bottom 35%. Then his PSA is at the very bottom - 0 %ile.
(It's also worth noting that it's probably Tatum's increased usage that has taken shots from DW. Because Brown's usage has always been in the 100th %ile throughout the season, but they've been using Tatum a lot more these playoffs.)

His Game Score, which is an
NBA advanced metric that John Hollinger created to try and calculate the overall impact a player has to a game, taking points, rebounds, assists, turnovers, FG%, fouls into account, it's been trending downwards, meaning his impact on the game has dropped to actually below his position average.

So I think the following things can be true: a) White is an additive player, he makes his team play better when there are players he can influence; b) he can't be relied on to carry a team himself; c) his impact on the game has dropped, mainly because his usage has dropped.
Now how to solve it? That's for smarter minds than I

Though if I had to put my 2c in I think he's just really lacking confidence, the team needs to involve him more to get his confidence back. They're trying to run actions for Vuc to get him more involved and aggressive too and it might also be affecting DW's usage.