Since Heyward came back from that concussion he's hitting .372/.404/.512 with a 6.4%/6.4% bb/k rate 147 wRC+. BABIP if you're curious is .390. What's interesting is that those numbers have come in a some what different way to the rest of his season. His batted ball data looks like this: 19.5% line drive 46.3% ground ball 34.1% fly ball 14.3% infield fly. His contact profile looks like 19.5%/51.2%/29.3% for soft/med/hard. It's only 47 PAs so not a great sample. But as a contrast to that his season numbers for contact are 17.7 % LD 39.5 % GB 42.7 % FB 18.9 % IFFB and his profile is 23.2 %/43.2 %/33.6 % soft/med/hard.
The numbers post concussion are more in line with what he has done for his career in terms of gb/fb rate. I'm not sure I have answers here but the two things that come to mind are A) was the early season data intentional(I think it was but idk) and B) is this post concussion data small sample or is he reverting some of what he may have done prior? For that second question, I wonder a bit if it's not some what natural. My working theory for pre-concussion numbers was he was hitting the ball too far under leading to lots more fly balls with good power but high fly balls that stay in the park aren't really great even if they have really high exit velocity. A natural thought would be to some what over correct and hit more ground balls.
What I will say is this, even if the numbers are returning to pre-2018 look, they still are some what different. That 29.3% hard contact rate is up quite a bit vs 25.5% in 2017 and 26.4% in 2016. Season in that range for him were 2015 with STL(29.1%), 2013 with ATL(29.7%) and 2010 and 2012 at 38.8% and 34.5%. For reference here, he hit .293/.359/.439 in 15 with STL. He hit .254/.349/.427 in 13 with ATL and .269/.335/.479 and .277/.393/.456 in 12 and 10. Those 4 years were 121 wRC+, 120, 121, and 134.
So while I was a bit more encouraged with the higher fly ball rate leading to even better numbers, as long as he maintains this sort of hard hit rate he's likely to be a pretty good hitter by the end of the year. I would also add that his K rate is really interesting. He's always been good there comparative to MLB average but he's on another level recently. Just to throw up some comparisons here, if we use those same 4 years of 10, 12, 13, and 15 his k rates were 20.5%, 23.3%, 16.6% and 14.8%. For the season as a whole he's at 11.3% but as mentioned that's dropped even further to 6.4% since returning from a concussion. We're legitimately getting to the point where you can start talking about him potentially leading the league in k rate. Last year the best qualified player was Joe Panik at 9.4%. Other names under 11.5% were Justin Turner(10.3%), Andrelton Simmons(10.4%), Jose Ramirez(10.7%), Yulieski Gurriel(11.0%), Mookie Betts(11.1%), and Melky Cabrera(11.1%). In 2018 he doesn't have qualified PAs yet but his 11.3% k rate would be 9th in the league right now.
