That depends entirely on texture size you have for each frame.
Each frame on spritesheet have 1px border around to prevent pixel bleeding.
Each frame of animation also should have 1px empty border around for antialiasing.
So when you have 5 frames animation and each frame is 64x64 then after exporting you will get a 256x256 file with a lot of empty space.
But if you make frames 62x62 then after export you will get 2 files: one 128x128 with 4 frames and one 62x62 with 5th frame.
And if you want your sprite to have nice and smooth edges, you need to add 1px empty border around your sprite. Which will make your actual texture 60x60 (while frame is 62x62)
If you learn how to use it properly then C2 actually is quite good with making the sprite sheets out of the textures on export. Just need to remember about some things while making your textures.
Like this green things on your first image. If they were 254x126 and be only 10 of them then you could fit 8 frames on one 512x512 and remaining 2 frames on 256x256 - no space wasted.
That's how C2 works. And all you can do is to accept it