Apparently, you have never tried to crack a safe, Metryq
The right way to proceed is not
to cut a man-sized hole in the door; this will take forever. The right way is to cut a tiny hole where the lock mechanism is, because this will take very little time, and then use that hole to open the door.
This regardless of whether the door is harder than the wall or vice versa. It's a simple matter of logistics: cutting open the lock requires you to cut thirty centimeters of bulkhead, while cutting an entrance requires you to cut three meters of bulkhead! The writers got that exactly right.
In any case, many episodes in TOS and spinoffs testify to the phaser-resisting abilities of standard bulkheads: there are many phaser misses that fail to do harm to the walls.