It is a question of opportunity cost. If you are studying openings at the expense of doing tactical puzzles and sharpening your tactics, it is not the most efficient use of your time at the 1200 level.

If you have a 1200 level tactics skill and 1500 level openings skill, you are going to be about a 1200 rated player. If you have a 1500 level skill in tactics, you are going to be about a 1500 rated player regardless of whether you've studied openings. Remember: Being able to calculate tactics better helps with openings! Just because your opponent has memorized something and you haven't doesn't mean you can't just calculate on the fly and avoid falling into obvious traps.