I normally add it like that, to not redraw, but the issue is NOT the drawing of events. It is the sync, after the backend returns.
My gif/video show this issue very clearly. We are talking a slow down factor of 10 on project.sync() before the scheduler is unlocked for further editing.
Just to be 100% sure i did it with your code, and sync is still above 10 seconds. On 5.2.7 and down it is 1 second for 300 events.