As suggested by Dani I am creating a new topic to request a feature.
As described here in the FAQ topic, I would like:
an understanding how a Gantt View Widget which is grouped by person is sorted
avoid automatic resorting
influence the order in which people are listed
On this note it would also be great to have more granular influence over the order in widgets in general. For example are subitems not automatically listed below their parent item nor are they grouped together. Instead more often than not one or several subitems of different parent items are interspersed between.