I own two 2016 BMW X3 35i vehicles. Both my X3s accelerate with authority.
One possible problem is the transmission in your X3 may have adapted to the sedate driving style of a previous owner. If you or your wife drive more aggressively over time the transmission in your X3 may adapt. You may also try to reset your transmission to factory settings as suggested in the link below.
https://www.bmw-sg.com/forums/thread...-10-mph.38817/
Have you tried driving your X3 in the sport mode setting? If so, does this make a difference?
You might also try adding a BMW fuel additive or Techron fuel system cleaner to your gas tank. This may help if the sluggish performance is related to deposits in the fuel injectors or system. Also, use a Top Tier fuel as recommended by BMW to help maintain performance.
https://www.toptiergas.com/licensed-brands/