See no reason why a light and puffy synthetic can not function as well as down in compartments using sewn-in baffle construction. Suspect that conventional synthetic constructions are used because they are much cheaper to produce. One way to find out is to try it. Also, the LiteLoft packed away years ago appears to have maintained its loft when checked from time to time.
In checking several suppliers for the Loftech as you suggested, noted that Quest has DWR treated 950 fill down for sale. But would still prefer a synthetic, as even the best DWR wears out eventually, and have doubts about how treated down will function when wet, as can happen no matter how carefully sleepwear is packed, The lightest and best synthetic I’ve found so far is Climashield Apex in a really great bag from Cumulus in Poland. But lighter may be possible with the baffle construction, using 0.5 oz sheer panty hose for the baffles. No MCP cracks please, as occurred when posted about lingerie baffles a while back. And the stretch may produce a baffle that does not have to be tailored to the curved shape of the the bag.
In the meantime, have continued to use a 20 oz Montbell spiral baffle down bag that keeps me much warmer than any of the much heavier synthetic bags used previously. So far no monsoons or tent failure have gotten it wet; but then do not camp in winter, or in tents or tarps that are not double walled, free of condensation, and allow dry entry and exit.
As the BPL forums have shown, many of the new materials are over touted, and do not pan out, especially when someone like Richard Nisley gets around to testing them.