especially since the wildzords are as intelligent if not more so than the galactabeasts and we saw them flat out refuse to fight despite being piloted

I think that's because there's only one Soul Bird, one heart for any given Gao combination at a time.

If the Rhino never came with the waist piece, how did it become the legs? Or was it so it connected with one but it still could with the other? I don't understand.

The waist piece only goes with the Gao Muscle Striker combo. It can combine with Gaoking without it and use Eagle instead.

The waist piece technically it isn't even needed. It fills in a the gap where the Eagle goes usually and adds stability.

but that makes no sense when gaoking didnt originally use it and predazord doesnt use it.

Exactly.

Soul Bird was pointless to actual combination. So the other animals should have been able to form Megazords and just not be as super effective.

But really at that point you've gotta wonder why the animals never helped out regardless of if they could combine.

Yup.

The combination pegs are attached to a metal rollcage on the Go-rhillar, and the Eagle (or disk) goes in there just for aesthetics.

man i need that waist adapter