Then Warspite, you're fully away that physical dimensions have almost nothing to do with combat capabilities. If it did, then RMS Titanic would have been a very formidable adversary.
However for warships, tonnage gives you a decent picture of a ships abilities, assuming it's designers are not, in fact, utter screwups.
That is debatable, as a Deutschland class cruiser cannot function at sea, when damaged, no matter how light this is. A hunter, chasing the raider can allow damage, as there will always be more hunters than raiders, given the British supriority in numbers. Since a Deutschland class cruiser was just that; a cruiser, with cruiser sized protection, all 6 and 8 inch cruisers could hurt her enough, even the little Arethusa, with her faster rate of fire 6 inch guns, compared to the lumbering, slow 11 inch guns on a Deutschland.
In other words, some of you completely ignore the fact the Deutschland class was designed to be a raider in the first place adn not a fighting ship fighting other cruisers. Mathematically the Raider in a hostile sea (Raiding in friendly waters makes no sense at all), with no supporting yards and ports to mantain her, on her mission, is at a serious disadvantage and cannot risk damage, no matter what sort of damage. Once damaged in a fight, the raider will get hunted down, due to her then known possition, while unable to run away from faster cruisers, that are theoretically inferior in gunpower, but can still hurt her hard.
Therefor heavy armament on a raider type of cruiser is irrelevant to her fightingcapabilites. The best raiders were never the heavily armed cruisers in both world wars, but the HSK typs merchant conversions the Germans also used. (Excluding the U-Boote naturally) These HSK ships had the firepower to take out a merchant ship, but not an allarmed warship (HMAS Sidney was fooled by the seemingly unsuspicious looking freighter when destroyed in a surpriseattack by HSK-8. All other encounters between a British cruiser and a HSK ended quite onesided.)
Deutschland was mostly a politcical statement to show the power of German ingenuity in shipbuilding, during the restrictions of the Versailles Treaty. Pack a number of battleship sized guns on a cruiser hull, something not done before since the ending of the Great War. Theoretically it overpowered any cruiser, but only in numbers, not actual figthing power. (Figtingpower is more relying on how fast you can deal a cripling blow to a target, to dicate terms. This required high rate of fire and this was not what the Deutchland class had. Also a larger number of guns, to compensate for the lwer rate of fire would have been nice, though not possible on a cruiser sized hull. 8 inch cruisers had simmilar problems btw, so either put in a larger number of them (10 in IJN cruisers in twin mountings to allow higer rate of fire, compared to the more cramped and slower tripple turrets on USN cruisers), or a QF type gun, mainly 6 inch.