If you think there's any good schmup on Amiga then you really need to check most of the PC ENGINE & MEGADRIVE ones
Also Amiga arcade games lack of variety/ideas or surprise in general, that's why Project X or even Battle Squadron are fundamentally (and retrospectively) sub par games, not bad but not as great as they are portrayed. In the context of Amiga games they're pretty good but as soon as one watches the consoles Schmups of that time they suddenly become rather lame (Apidya escapes this
The Factor 5/Kaiko guys probably made the best arcade games on Amiga (Turrican series, Apidya, B.C. Kid) due to the fact that they really cared about what they where doing and that they were strongly influenced by the japanese console games.
Any arcade game running at 25fps doesn't deserve to be ranked among the best anyway, and for a schmup it's a fatal weakness (imagine the Turrican series running at 25fps !).
Jerkiest scrolling: Thexder.
Schmup made in C with a rather smooth animation: Sidewinder (was even entirely made with ROM libraries).