The holes at the bottom of the atomizer are going to restrict airflow far more than the cartridge airholes.
Check a 510 battery. There are usually 4 shallow slots (OK, there are 4 on all of my 510 battery connectors, other may differ, I don't know). Check the atomizer, just above the
threads that screw into the battery. Both of mine that I'm looking at have 2 holes.
Those slots and holes control the airflow. The airflow
through a cartridge is much greater than through these holes. And a cartridge isn't exactly airtight where it fits into the atomizer, either.
Bring a 510 to a hardware store and try to find a file that will fit into the slots in the battery. Make one bigger. Find a drill bit slight larger than the holes in the side of the atomizer. Make one bigger. For both, those are very small openings, so it won't take much to make them bigger. Finding tools of the correct sizes might be difficult though.
If the airflow is too much, vapor production will drop. If this happens, try covering one or more of the slots with some Scotch tape or something. It might also help to seal the cartridge-atomizer joint, too, to make sure that all air is coming through the atomizer.