Until now, we've been told that Kelpiens are hypervigilant and constantly aware of threats, with a finely attuned survival mechanism and great speed, all as a result of being a prey species that has to use its wiles to ensure its own survival - but here they're shown essentially as domesticated and docile, and willingly lining up to be killed (by who?) as part of an ingrained religious system. This goes against what we learned in season 1.
The beacon technology essentially falling into Saru's lap, him being able to use it to not only send a message but establish a dialog, and Starfleet being sent to rescue him and him only from the planet, are all highly contrived. Yeoh is a welcome presence but Georgiou's dialog is terrible here. Saru's relationships with his father and sister are also poorly sketched and incredibly formulaic. He has conflict with his father, who's conservative, rigid and loyal to tradition, but feels protective of his sister, who's innocent and pixie-like. (Gee, where've I seen that dynamic before, apart from every formulaic family drama ever?)
The idea of Saru as some agrarian peasant from a pre-warp society plucked from obscurity because some technology fell into his lap goes against what we've seen of him so far and doesn't serve his character well. Doug Jones is a fantastic actor, and I maintain that Saru and his race have tremendous potential, but that's wasted here in favor of an incredibly generic origin story that even seems to contradict what we knew of Saru and the Kelpiens.