So Luzardo has been compared to Trevor and I see that they have basically the same 4 pitch mix. (Luzardo has a curveball, but it spins like a slider so it has more of a look of a slider. They both have similar numbers in the minors and Luzardo's struggles this year as a starter (7 starts, 28 innings) look similar to Trevor's in 6 starts last year.
One of the biggest things that Trevor has done is to ditch his sinker, which was his worst pitch to go to a 3 pitch mix. Trevor's whiff% and exit velocity on the remaining pitches are about where they were last year, but without the sinker, hitters are doing far less damage. Luzardo's worst pitch is actually his 4-seamer. He has gradually increased his use of it and hitters are taking advantage. I don't fully endorse him dropping it completely, but I do think it would be a good idea to rely more on the sinker with the 4-seamer coming out more sparingly. He could also work on mechanics as perhaps he is tipping something. Combine this with improving the changeup, which our guys have a knack of doing and I feel that Luzardo will be fine.