IOS-XE is able to have better logical and especially physical separation of the three planes.
For example a chassis is able to have 3 blades, one dedicated to control plane, one to data plane, and one to the management plane. Granted that is a glorified example, it’s possible.
Since IOS XE runs a linux operating system it is able to take advantage of multi-core processors. Now speaking on the smaller tier hardware, we still see quite an improvement.
We are able to set affinity to certain processes and make sure they are isolated on certain cores. This is crucial when talking about separating the mgmt/control plane with the data plane and ensuring they cannot overwhelm eachother. It also helps that now the dataplane isable to take advantage of other cores and use them for forwarding traffic. This is the multithreaded ability we did not have with monolithic IPS.