Hey Kendo Team,
you already have a solution in jQuery for my problem (https://docs.telerik.com/kendo-ui/knowledge-base/grid-group-remove-footer-header-one-record).
Unfortunately this solution did not work in Angular.
Desirable solution would be a flag in GroupHeaderTemplate which removes header if group size is one.
Another solution could be; allow a class field in GroupHeaderTemplate, so that we can set display to none if group size is one.