Unity 2D Game: does transparency count as overdraw?

I’m working on a 16:9, 1920×1080, 2.5D point-and-click adventure game and I just today learned the word overdraw. I have a few questions, but first some details about the game:

Backgrounds

Backgrounds are hand drawn, and broken up into layers. For instance, if there’s a room with a table, some chairs, and a lamp on the table, then I’ll have a sprite for each of those objects whenever I want the player to be able to walk in-front of or behind that object.

To make positioning of these objects consistent with what’s in photoshop, I’ve exported each layer as a full HD image with huge swaths of transparency. These images have a very small memory footprint because only a small portion of image is populated with non-transparency.

Animation

Animation is hand drawn. To make character position consistent across all characters, each animation is exported as full HD images with huge swaths of transparency. The characters reside at the bottom center of frame. I call it the anchor point. In point of fact, it’s where I put the pivot.

I’ve got all animations and backgrounds in sprite atlases to save on video memory. So far, it’s low.

MY QUESTION:

Am I a huge idiot? Are these full screen images with lots of transparency going to be a big problem for me? The game is for mobile and PC and Switch.