I think it's fine personally. The ability is very strong in a team game if you have good map awareness and/or communication with teammates. I believe the slow missile speed is an intentional mechanic to give enemies a chance to react, since there is no counter-play available in the form of dodging, or having a teammate block the attack.
Your suggestion for an upgrade to Regula 3 missiles gives me an idea though. What if the missiles changed with ranks of the ability? Regula 1 at level 5, 2 at 10, 3 at 15. They could have some minor effects. Regula 1 would be the current version, 2 could have a slight increase to travel speed, 3 could add a small area damage component. Might be interesting.