Summary
Four seasons in, and Bagley has not lived up to the hopes that the Kings had for him when they drafted him second overall in 2018. Despite having some skills on offense, Bagley has been a very inefficient scorer. His shooting percentages at the rim are decent, but his midrange efficiency is poor. He also hasn't shown any ability to make plays for others, which makes his inefficient scoring that much more damaging, considering scoring was supposed to be the one thing he did well.

However, Bagley did have a decent showing with the Pistons after being traded to Detroit. He started to get a lot more assisted buckets near the rim, and his overall efficiency improved because of it, as he shot 78% at the rim for Detroit, according to Cleaning the Glass. Bagley got more lobs and easier dump-offs than he did in Sacramento.

On defense, Bagley is caught between positions. He doesn't provide any rim protection, which makes it difficult to play him at center, but he also doesn't guard well in space, which makes it difficult for him to defend power forwards.

If Bagley can become a better pick-and-roll finisher, he could carve out a nice career for himself as a 6th-man scorer type, similar to what Montrezl Harrell has become. On the other hand, if Bagley doesn't develop quickly, he could even find himself out of the league in a few years.
 
Cap Considerations
Bagley will be a restricted free agent with a $28.3 million cap hold and full Bird rights. Since Bagley did not meet the starter criteria, his Qualifying Offer will be $7.2 million.

The Pistons may refuse to tender him a QO, making him an unrestricted free agent. With Bagley's QO being on the higher end, I think there is a possibility this occurs, but if the Pistons like Bagley and don't think they'll have a better use of their cap space, they may tender him a QO in hopes of re-signing him on a reasonable deal. If the Pistons do give him the QO, Bagley may consider signing it right away considering I'm not sure he'll get a better offer than that.

Other teams will have multiple ways to sign Bagley as even teams without cap space could possibly use either of the Non-Taxpayer MLE, Taxpayer MLE, or possibly even the Room MLE to sign him. However, Bagley being a restricted free agent would greatly lower his interest among teams, as they will worry that the only way to pry him away from Detroit would be to significantly overpay him.