Yangti higher than togal? Who told you that?
The yangti tantras.
So what makes it higher than togal?
More methods, special methods, not taught in tögal. Even so, there has been some bleed over. One finds some methods of Yangti in cycles like Gongspa Zangthal and so on. Tögal is like the base for Yangti.
The simplest way to put it is that sems de works on with mind, but not with visions. In terms of the four visions klong sde works with space, but not with light. Tögal works with light, but not with dark. Yangti works with dark and other special methods which work with light. Since klong sde works with the four visions, this is why it is asserted that one can obtain rainbow body with klong sde. One cannot obtain rainbow body with sems sde.
This also the reason why it is asserted that one cannot obtain rainbow body with mahāmudra lacking tantric practices connected with the wisdom winds. I don't expect you to agree, but you should be aware of the reasoning.
Further, the yangti tantras assert that yangti is utter pinnacle of Dzogchen practice and theory. Perhaps the most famous yangti cycle is that of Dungtso Repa. The late Khetsun Zangpo was famous as one of the main promulgators of the Dungtso Repa Black Yangti teachings.
There are yangti cycles by Guru Chowang, Ngala Padma Dudul, Rigzin Chanchub Dorje, and so on.
As I keep stressing, there is a lot more to Dzogchen than Yeshe Lama and Thigle Gyacan. Can people obtain awakening from Yeshe Lama? Of course. Is there always more to learn, etc. Yes.