Thanks all for the info. It helps.
Re: #2. It's more likely I'm missing something. My concern with larks heading the fixed loop to the strap is sometimes I end up with two trees that are closer together than one would like. I end up using a marlin hitch and a biner (descending loops Garda hitch suspension) do I'm imagining that the buckle would replace the marlin hitch in those situations. Or would the whoopie sling be able to shorten up dramatically. Sorry if it doesn't make sense as I'm trying to imagine it with limited experience with whoppie slings.
There are a number of creative ways to shorten things up with whoopies, I've threaded the whoopie through the loop on the tree strap and run it part way around to the side of the tree to my Dutch buckle. Just so long as the back half of the tree is protected by strap, that is where the vast majority of load is.
Also I've brought the adjustable end of my whoopie down to a small loop and larks headed it over the gathered end of my hammock leaving a shorter loop that I can hang over a marlin spike arrangment on my tree strap.
These are just a couple of ways to go YMMV.