2016 H-1Bs [1] - 398718 submitted with 53456 denied = 13% denial rate
2017 H-1Bs [2] - 403675 submitted with 37993 denied = 9% denial rate
So it looks like the denial rate has actually decreased.
[1] https://www.uscis.gov/sites/default/files/USCIS/Resources/Re...
[2] https://www.uscis.gov/sites/default/files/files/nativedocume...
On the first table, it shows the total submitted is 398,718. The number approved is 345,262, which leaves at most 53,456 denied (398,718 - 345,262 = 53,456).