I can see why you had some pace related problems with the powerhouse chem style, i personally used him with an anchor to boost the strength a bit and he kept being overrun quite often. However as soon as I switched to a shadow, he just caught everyone and locked down the right side of my defence. He did not even struggle against speed demons like Al Owairan or Mbappe
I can relate to the issue with the chemstyle-switch, I used flashback Icardi with an Engine applied to him (same problem that you had with Vlahovic, I thought he would feel to clunky) and he was incredibly bad, good inside the box but still turning like a tractor. Then I applied a Hunter chemstyle on him and he has been incredible ever since (about 270 contributions in 150 games)