I did some DB testing on my own and Distortion Pierce isn't as good as Light Wave because of its big aoe coming form the side, this means you can easily hit something other than the weakspot, especially on Bosses like Rockbear that waves their arms / etc. on the side a lot. Light was is far more reliable on bosses like these or those that turn a lot.
And most of Distortion Pierce's damage comes from that big aoe scissor part of the pa whereas Light Wave' has several hit that add up to more damage than the final one so you can easily adjust your position to keep hitting the weakspot and even if you miss it with the final hit you don't lose nearly as much damage as with Distortion Pierce.

Also Vertical Flow and Radiant Sting are notably weaker than Distortion Pierce / Light Wave.

PS: gotta love the broken mess that is Lockon, had to quit a try cause switching from the auto-lockon to Rockbear's belly to his head my me instead lockon to the previous in the distant corner and Radiant Sting made me shoot past the Rockbear I wanted to attack.
I'm used to it being crap but this kind of total fail, changing to another target at a 45° angle when at 0° there are two right in front of me is kinda rare.
Sadly it doesn't matter how often I tell Sega to fix it during surveys, they just don't care.