Lantz is one of the most knowledgeable coaches I know with respect to teaching the lower half. Not sure there’s anyone better as a matter of fact.
Driveline is the most knowledgeable with respect to helping arm action and efficient movement patterns (among other things). Driveline is at the forefront of pitching research and instruction currently.
I wouldn’t hesitate to have my kid work with Lantz in a camp. My son has gone to Lantz’s camp once and he’s worked with him one on one too for a few hours.
However, the most important thing is to keep working on stuff outside the camps (which I’m sure you know–just reiterating it). The biggest thing I’ve found is players think a camp is going to fix stuff. It’s only the beginning. Fixing things or improving things requires a ton of work outside the camp. Take notes, shoot video, learn stuff and work on it.