Hey there,
this is done on purpose and matches the description. The base game has one major struggle when it comes to railguns: There is no point in researching railgun damage above level 2 (they one hit all asteroids) and there is no reason to research rail gun speed above level 7 (the animation doesn't become faster).
Giving the player an alternative projectile that deals 10% of the damage in 10x the radius fixes this and gives an incentive to research further damage upgrades.
Depending on player feedback I might give them an additional explosion at the first target they penetrate or similar effects in the future.