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)
"With sudden enlightenment to Tathagata Chan,
The six paramitas and myriad means are complete within that essence."
(Yongjia Xuanjue, T2014p395c14; tr. from "The Sword of Wisdom")