This is part of the biggest advantages of Android's operating system, based on open source, but also disadvantages.
(Well, in personal opinion I think the advantage is much greater. :P)
For these reasons, the 'smoothness' can vary according to the firmware even if it is the same launcher. Since each of the launchers on the market has different implementation of the animation used when switching screens, a firmware will has a launcher of which chemistry fits well.
Therefore, it should not be assumed that a launcher is not well-optimized because it has so many lag on my current device. It can be the most smooth launcher for another firmware.
ssLauncher has the following 6 options related to this 'smoothness'.
1. 'Scroll wallpaper' in menu > preferences: It can decrease the smoothness. (May not be effective depending on the firmware.)
2. 'Buttery smooth' in menu > preferences: It can improve the smoothness dramatically. (May not be effective depending on the firmware.)
3. 'Less memory' in menu > preferences: Generally it can decrease the smoothness. But it can remove the lag by high memory use on the device with high resolutions.
4. 'Type' in menu > theme > animation: The smoothness is varying according to animation type.
5. 'Hide frame' in menu > theme > animation: If this option is checked, there is quite a bit of smoothness improvement.
6. 'Use GPU rendering' in menu > theme > animation: This is enabled from over Android 3.0 for some animation types. However, please keep in mind that hardware acceleration does not always guarantee the smoothness improvement.
As I mentioned earlier, the effect of the options can vary depending on the firmware. So you should find the best option set for your device.
Try it now. :)