As of today, the activity log doesn't represent all of the activities undertaken on the sheet. For example, if a row hierarchy or conditional formatting has changed, columns formatted/hidden/unhidden or removed, it won't show up on the activity log in detail. This is difficult when we are trying to investigate the root cause of an error. See attached screenshots.
The activity log, as the name indicates, should provide all details.
Ipshita Mukherjee