Hope the answer below is not too serious for this post! LS is "fast" compared to mechguns, but is "slow" compared to handguns; mechguns' 9 bullets can probably be fired faster than Last Swan, but has a long recovery; LS is rigid in that it only allows another button press after all 3 bullets are fired, while normal handguns allows button press after 1 bullet is fired, making those faster.
Hence the proper weapons to compare it with, I think, is Charge Raygun and Heaven Striker. Last Swan's strength lies in its innate high multiplier (3x N attacks, 3x1.89x H attacks) compared to sacrificial guns (1x N attack, 1.89x H attack, and 3.32x S attacks). On the other hand sacrificial handguns has higher base ATP, can have hit, can glitch bullets at range, and is faster as explained.