Would you exclude Vajrayana from Mahayana? Shingon was removed from the Tibetan area years ago because they are two different systems with different history, and it was suggested by some Shingon followers who found the unending comparisons and such with Tibetan Vajrayana tiresome (IIRC). Tibetan and East Asian exist separately because they are distinct historical developments of Mahayana with several significant differences between the two, while the two groups share a lot within their own area. If anyone wants to discuss this topic about the differences between major Mahayana groups please open a topic for it in the Mahayana forum.
"If the Buddha-Nature is seen, there will be no seeing of a nature in any thing."
(Nirvana Sutra, T12n374p521b3; tr Yamamoto)
"Neither cultivation nor seated meditation — this is the pure Chan of Tathagata."
(Mazu Daoyi, X1321p3b23; tr. Jinhua Jia)
“Don’t rashly seek the true Buddha;
True Buddha can’t be found.
Does marvelous nature and spirit
Need tempering or refinement?
Mind is this mind carefree;
This face, the face at birth."
(Nanyue Mingzan: Enjoying the Way, tr. Jeff Shore; T2076p461b24-26)