Not a problem because Cerys is a Heavy tank and she doesn't need penetration while Diane is an artillery so she hits big numbers to the point if she crits she can one shot some tanks. Pen also doesn't do much as most tanks that you shoot at dont have much armor except their heavies which gets shredded through Valor emblems for tanks like stridsvagan, type 59 or any medium with decent attack speed. 3*s just get obsolete so fast.
For the blurry scene issue I wasn't the only one who filed a report on it according to the devs so it is an issue they are working on.