Summary
Diallo had a bit of a breakout year in '20-'21, increasing his scoring from 7 points per game in 19-'20 to over 11. His usage went way up, and he had some big scoring games throughout the season. However, these numbers came while playing for two of the worst teams in the league that season, so it's hard to take too much away from them (to be fair, the Thunder were actually decent during Diallo's time there). While he didn't take any major strides in '21-'22, his production remained similar to the previous season.

Diallo lives at the rim, as the majority of his field goal attempts come either at the rim or in the short midrange, according to Cleaning the Glass. Diallo using his quickness to get to the rim (and the free-throw line) and can do damage as a straight-line driver if he's given a lane. However, he hasn't developed much of an outside shot yet, thus leaving him below average in eFG% for his position. He shot just 24% from three in '21-'22, and for his career is under 28%, so he needs to improve those numbers to really be a threat from outside.

Defensively, Diallo is quick, but he's fairly skinny, and is not someone you would want guarding forwards with bigger size. He's better off guarding down a position and using his length and quickness to bother opposing point guards. He is disruptive on defense, consistently posting high block and steal rates over the course of his career. He also rebounds well for a wing on both ends of the court.

Diallo is still only 23 and has received solid minutes for the Pistons, so I expect they would pick up his option for '22-'23 unless they really need to maximize their cap space.
 
Cap Considerations
Diallo has a $5.2 million team option for 2022-2023, and if that is declined he will be an unrestricted free agent with a $9.9 million cap hold and Full Bird rights, meaning the Pistons would have no restrictions on re-signing him.

If he becomes a free agent, other teams will have multiple ways to sign Diallo as even teams without cap space could possibly use any of the Non-Taxpayer MLE, Taxpayer MLE, or possibly even the Room MLE or Bi-Annual Exception to sign him.