Is gluing table top planks better than using pocket hole screws?
A properly glued panel will be significantly stronger than a panel that is joined only with pocket screws.  That being said, pocket screws can still be useful to eliminate the need for clamps while the glue dries.

A single panel (like a tabletop made of several planks of wood glued/screwed together) will expand/contract as a single piece, hence why the need to join the table top to the apron using a fastener that allows the panel to expand and contract.