This is definitely something that needs to be looked at by the devs, but if you place the first flights yourself in a spread of landing and departure timing, the auto scheduler will plan flights following your initial setup. You can also manually re-schedule flights to spread them out more.
Would be nice (for a quick fix for this issue) if we not only could set the separation time in between flights for stands (as it is now), but also to set the separation time for landings and take-offs.
There is also a feature voting for a more enhanced flight scheduler posted by @88ekke.