Hello Alberto,
I am afraid that the required automatic line-height appearance could not be achieved within the Gantt chart. Even if that is possible for the TreeList part of the widget (the left-hand side), that would result in a mismatch with the Timeline view. Having that said, the only option that I could offer you is to set a higher default RowHeight for all the rows in the widget.
Also, I have converted the current thread to a feature request in our Feedback portal. I would suggest you cast your vote for that. Based on the support it receives from the community, we will decide on whether to proceed with its implementation or not.
Regards,
Veselin Tsvetanov
Progress Telerik