Kevin Long has supposedly been working with Wieters trying to get him to use his lower half more. The old saying "if it ain't broke, don't fix it" doesn't apply here.
You can see a difference in his swing on the HR the other day
vs that grand slam he hit in Chicago
https://www.mlb.com/video/wieters-grand-slam-to-center/c-1695631183 (yes I know it is from the opposite side but it's the best sample I can find of how weird his swing and especially his follow-through got)
The swing in Chicago is all shoulder and upper arm, and the ST shot you can see his feet aren't moving around as much and he's swinging more from his core and his lower half. That's more consistent with how he was swinging early in the 2017 season (and he was batting .273 through the end of May). He is INCREDIBLY strong if he can lob one out on a shoulder-driven swing. If he can keep his feet planted and swing from his thighs, he'll have good numbers this year.