The shotgun is also one of the few weapons you can easily projectile boost by blue punching the shot (which you can't do with the railgun, since it's much more usable with the coin during high speed fights in turn), which also turns it into a makeshift sniper if you're willing to learn timings and applications. You can do a lot of different things, but they require some deeper interest in how the game mechanics work and a drive to maximize efficiency, rather than just getting the job done in a binary sense. On a lower level, the shotgun's explosion is also more efficient than the railgun's at building speed and gaining movement advantages, since you can effectively blast jump with it by shooting down.

You're really looking for the best way to get things done in each situation and environment, rather that just getting to the end of the level.