I dont agree.
I have very little lag with jailbreak on my iPhone 4.
Im aware that winter board and the amount of themes downloaded causes this on my particular handset, but I'm willing to put up with this for the theme I'm using. I know this as uninstalling winter board removes any lagg, so its not the several tweaks etc I've already downloaded.
One of the usual pieces of advice is to uninstall recent downloads one by one until you see the lag go.
hopefully future updates will see this better resolved.
oh and another piece of advice is to install the barrel tweak as this softens the lag, possibly.