Yeah, it seems like it would be possible for the DB engine to aggregate all these increments into one update. If you have two increments by one each in the queue, why not make it a single increment by two? I'm not sure though how much computing power it would need to figure that out...

wouldn't that break the atomic and isolated rule of ACID?

Not necessarily. If both updates are in a single transaction then it's valid for the query planner to batch them, although that seems unlikely in the use case this table layout is designed for.

Not any more than the slotted counter pattern...

how does the shape of data impact the storage applications safety contract?

The DB could figure it out IF it had monoid counter type to use as the column's type.