Many airports use a rolling departure. Depending on the ac, some of the 4 engine variant take some time to balance.
Same issue on roll time, some take a bit of time to get moving. Yes, of course, there are plenty of airports where the follower cannot see the leader rotate. Pretty sure that ATC can see the aircraft rotate, and there is the weight off wheels broadcast.
There is wake sep, and there is the min sep to consider.