its not really lag tbh.
So on other bodies the camera is blacked out for the period of time the shutter closes.
With the stacked sensor bodies you can do blackout free shooting. So if you are using very long shutter speeds it will seem "laggy". On any other camera you'd just have a longer blackout.
its not really capped I think, its just the limitation of the older processor
You can checkout some speed tests here.
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For A1 take a look at A7SIII tests which has the same new processor (so speeds will be roughly the same).