In 802.11 (CSMA/CA), does a higher data rate imply more number of collisions?
The premise that a higher raw data rate implies a higher packet rate is false. The packet rate would only go up if the network were already saturated with traffic, and the application actually transmitted more packets as a result of the increased available bandwidth.

All other parameters being equal (packet size, payload bandwidth, etc.) a higher raw data rate means that the individual packets are shorter in time, resulting in fewer collisions, not more.