I feel like the reason a lot of games are slow right now is because they are built out of these huge abstract "everything-doers". For example, each button can be configured in millions of different ways even though the game usually only has a few different types of buttons. It's not an optimal data structure by any means.

It's not like in the olden days where you would blit this stuff out to the screen using specialized routines that scream along as fast as the CPU will let you. Now, everything is dynamic and multipurpose and configured using properties on the object... engines like Unity get away with C# and way too much runtime reflection because it's convenient in the editor. Developers like it, it's less difficult than writing specialized routines.