You could do it fine with waypoints and triggers except for the timing. To make a good cutscene it has to be right to within about two seconds, otherwise either the camera shot misses the action or the player is watching something not happening, which is confusing and/or tedious.
The game engine is very sophisticated when it comes to gameplay, and it is this sophisticating that gets in the way of cutscene making.
Even if you could get past the game engine limitations, you still get problems resulting from different computers having different setups. Cutscenes can be very demanding on the computer (partularly if you have rapid changes from one part of the island to another) and some kit is better than others. In other words, even if it works on your computer that doens't mean it will work on somebody else's.
Consequently, the more precise you can be in your instructions to the units. Waypoints and triggers are too vague in this context. On the other hand if the plane is setpossed into a position relative to the chopper, and the camera is also relative to the chopper, then you've got a good chance of making it work.
I wouldn't use createUnit for this because you have the hassle of making the plane fly. Just have it cruising somewhere.