No watch has true "instant pace". It is all computed in arrears and is a balance between responsiveness and smoothness. A longer lag time gives you smoother data but is slow to react. A short lag time gets faster responsiveness but choppier data. TomTom is slow to react to changes in pace because it applies a long smoothing period to produce smooth, non-choppy data. If you are running at a steady pace you will not notice the lag. However, if you are doing intervals or sprints or changing speed a lot the lag can be become more apparent. This has been a complaint since the first version of the watch was released 3+ years ago and really has not changed much, so I would not expect much to change now. If this is a vital feature for you and you are within your return period you may want to look at other devices that offer this option now. I would not count on it coming, you need to make your decision based on the features that are currently offered, and not what may come.
They are using a slightly different data series. The pace is showing a specially smoothed pace - this is the values that the watch is showing in the pace screen. Unfortunately, the smoothing can cause the average values to be slightly off. If you want to avoid this, you can use the lap pace or the average pace field on the watch, which will align directly with the split / lap times. To summarize, the split times will be more accurate than the pace shown in the graph.