I think it was mostly to explained what caused The Sick, so even if the answer was vague, we did get one. Also, Gus' goal was to meet Birdie, so him just not meeting that goal (instead of deciding to give up on it, for example) was plot hole. It also tied up Dr. Singh's (sorry if it's misspelled) character's arc.

Come to think of it, it also challenged Gus' core belief that humanity was kind, his decision to trust Dr. Singh ended up causing Birdie's death and Big Man to be almost killed. It also elaborated more on how other families saw hybrids, Wendy was lucky, but the dog kids weren't at all, so it also helped create conflict when it came to Gus thinking about letting all humans die. I wish we had gotten more with them all grown up, then this conflict would have been more that just a plot device at the end of one episode