Eastern Sino-Tibetan is not a true branch, but is a cover term for various diverse independent Sino-Tibetan branches that had been splitting off from Proto-Sino-Tibetan from the early Neolithic late into the Bronze Age. It is a paraphyletic. Hence, "Proto-Eastern Sino-Tibetan" would be equivalent to Proto-Sino-Tibetan itself.
Eastern Sino-Tibetan branches contain the most diversity, and are the result of the initial spread of Sino-Tibetan-speaking hunter-gatherers expanding both upstream and downstream (west and east) along the Yangtze River drainage basin during the early Neolithic. This early expansion spread out of modern-day Sichuan and Yunnan westward into Arunachal and eastward into the Three Gorges region (Tujia-speaking area), the Middle Yangtze region (Donor-Hmong-Mien), and the Yellow River Plain (Sinitic). The migrations would have been star-like, resulting in complex linkages. Similarly, the Trans-New Guinea and Indo-European language families had undergone "star-like" expansions during the Neolithic, resulting in many branches that usually do not form clearly nested structures.
The Western Sino-Tibetan linkage and the Bodish linkage split off from Eastern Sino-Tibetan during the Neolithic. Multiple streams of westward migrations resulted in complex linkages containing various areal features but no single unitary features or isoglosses suitable for meso-level reconstructions.