For the most common apps, no, it's not slower in my experience on Nexus 5, 7, 10 and some Samsung tablets.
For older devices, there are performance improvements in the ahead-of-time compilation with upgrades in major versions of the OS.
That helps. Lack of multimedia hardware support for older devices in newer apps can still be an issue.
Running Lineage OS 13 on a nexus 10, I see great performance for all the default apps and google apps. The main source of performance issues I see is apps that do not support the multimedia hardware (eg. arm neon on Nexus 10). Some video apps such as Directv now, HBO GO don't use neon, overheat with high cpu use as a result. Those that do support neon work great, including Netflix and Hulu. So it also depends on app support for hardware.
For older devices, there are performance improvements in the ahead-of-time compilation with upgrades in major versions of the OS.
That helps. Lack of multimedia hardware support for older devices in newer apps can still be an issue.
Running Lineage OS 13 on a nexus 10, I see great performance for all the default apps and google apps. The main source of performance issues I see is apps that do not support the multimedia hardware (eg. arm neon on Nexus 10). Some video apps such as Directv now, HBO GO don't use neon, overheat with high cpu use as a result. Those that do support neon work great, including Netflix and Hulu. So it also depends on app support for hardware.