Ofc he knew of kkg ability that doesn't mean he can do it without their blood lime limit, and there are really only 6 KKg ability in leaf, hyuuga, shino clan, and ino clan, nara clan, uchiha, and choji clan that has bloodline limit. you are comparing bloodline limit to thousand more ninjutsu, gentjusu, and taijutsu jutsu.
first of all when kishi made his own characters say a person mastered all the jutsu in his leaf it means he know and has counters for every single one of them if he doesn't know them. So if anything you are question kishi writing since he made like 5 dam people say hiruzen was OP. ( you know what i realize when you say KKG i think you should re look most of them seeing how Uchiha's had fire nature which let them use fire tec which other people can do, because its a ninjutsu--Hiruzen had fire nature he knew all those. the only argument you have in saying hiruzen don't have is Rotation, nara shadow, and the ability to make bug live inside you and maybe even expansion jutsu. but really sharingon ability is not really you want to argue against him seeing how you have to be born with it---The writer stated "leaf jutsu" not "clan Jutsu"
----If you want to talk about Rasengon, well here is the kicker-Jman did it right? the 3th grandson did it correct? did you know sarutobi clan is state to have the ability to master every high lvl tec with ease? that's their bloodline limit. Sarutobi seen death seal once's and could do it with so practice, i am sure he seen rasengon and chidori and knew how to do them, that doesn't mean he want's to rep other people jutsu.