To my recollection, virtually every slab holding the comic books I have had graded since I have done so has flaws. However, prior to approximately 2018, if memory serves, the flaws were typically minimal. Since then they became more significant, including, of course, newton rings, very visible and often deep scratches and/or scuffs, spots, debris inside the holder with some being quite large, comic books moving far too freely inside the holder, cracks in the holder, etc.
Yet, I keep paying for CGC's services and will likely continue to do so. Clearly, I'm a born sucker.