The cautionary animal rights dystopia was the closest this series has come so far to dropping anvils on its audience's head

Yes, and, I mean, as morals go, it's "don't mash up all your animals into one and then make them vivisected cyborgs to power your time machine". Which is ... highly specific.

it comes with the aura of a cult classic for me, where it's huge for the people who found out about it and for the people who didn't, whatever.

That's my impression too (as someone who was just too young to see it the first time round).

I have also been informed that its unplanned cliffhanger ending is even more ridiculous than Sapphire & Steel's due to real-life meta.

I actually find its ending perfect for the show (though Sapphire and Steel's also sort of is, though it's more visibly a cliffhanger). The ridiculousness is more in the nature of the subject matter and the possible reasons for the creator's disappearance.

... I have no Sandbaggers icon and this is suddenly outrageous to me.