I don't really see most of the other shots as underpowered myself, more just "different and underappreciated". Most of them have some sort of utility to them, even if one is more versatile/powerful overall. Sure, a couple like MoF MarisaA or UFO MarisaB are flat-out garbage, but many are quite decent. Marisa/Youmu/Remilia solo and Netherworld Team in IN are all pretty decent and underused. PCB MarisaA has the strongest far shot, which is nice, even if she has fewer bombs and awful range. MoF ReimuA trivializes stages, and MarisaC is quite good if you're used to her. MarisaC makes a great survival shot in SA, ReimuB has the ever-loved homing (plus autocollect),. MarisaA trivializes Nazrin's last card and Kogasa's first (and I'd assume Nue's UFO cards), ReimuB's surprisingly good for being the second-weakest shot (plus the smaller hitbox is nice).
Obviously one shot will be preferred for being the best, but the others are still decent in their own right. In some cases, I actually prefer the "bad" shots for their abilities, particularly the homing and spread shots. IN Marisa Solo being another of my favorites, since she gets all her Marisa power without getting crippled by Alice whenever she focuses