As a director who had used both 2D and 3D, I can tell you're not in our industry, nowhere near it as you can't even think in terms of why you'd want to use either, and chances are you're probably just a kid who bought Dawkin's animation book.
Go ahead and draw 30 seconds worth of a dynamic shot, 30 seconds at, I'm being very kind here, 5 frames per second, that's 150 frames
150 frames of pencils, 150 frames of clean up for it, 150 frames of colouring
Then it's 150 frames of the background (assuming there will be only 1 BG plate, not multiple because I'm nice to you), colouring/painting 150 frames to put behind the earlier 150 finished frames of your character
How long would that take?
That's right, just as long as it takes to model, rig and light this scene in 3D, and we can make it look even more realistic, and with more detail (+we can keep going, not just 30 seconds)
In an actual pipeline, pre-production is slow on 3D, but everything else is much faster compared 2D