Indeed, this graph here
is quite wrong. But not necessarily "utterly wrong".
It is just very speculative, and should probably be marked as such. Most "Pure Land Buddhism", in its contemporary form, is not at all the Pure Land Buddhism speculated to have existed in Ghandara ~0-200
AD. For instance, the traditional Indian Pure Land Buddhism still involved the following of prātimokṣa and bodhisattvaśīla, two practices generally discarded in Pure Land Buddhism today.
I myself would place the ascendence of contemporary Pure Land around ~4-600
AD, as exemplified by when it entered into China and started to gradually take its modern-day form.
Similarly, Mahāyāna's beginnings are much more mysterious than what the chart implies.
For instance, all of the Sarvāstivāda & Mūlasarvāstivāda monks converted to Mahāyāna, then
some converted to Vajrayāna when it began to become popular in India. It seems here that they all converted to Vajrayāna.
Another issue is ordination lines vs sects. The modern Mūlasarvāstivāda that "became" Tibetan Buddhism was not a 'school' anymore, given that they were fully converted and discarded their traditional Sarvāstivāda beliefs and theories of the Buddhadharma, rather, they were a vinaya lineage of ordination, I believe.
If Mūlasarvāstivāda is listed as "becoming" Vajrayāna, than Dharmaguptaka (once again coming from the Sarvāstivādins again), not Mahāsāṃghika, should be listed as what "Mahāyāna" came out of, as all modern Mahāyāna ordination lineages trace themselves to the Dharmaguptaka.
