I just put together a build out of parts I had on hand with a goal of slimming down the weight a bit.  Faxon pencil profile 16" barrel, magnesium lower, Aero Precision upper without forward assist, and a few other light weight parts.  Some of the savings offset by the Fostech Echo-II, the heavier carrier in the Superlative mid-length piston kit and the Magpul CTR stock.  The Fostech will get swapped out after the next Geissele sale.  Weight before flash suppressor and sights/optic is 5.46 lb. which is lighter than everything else I have except possibly the .22 LR FrankenPlinker.  So, is 5-1/2 pounds a decent mark for lower weight without utilizing a minimalist stock or composite hand guard?

This is not bad at all.

I have a buffer less AR with a middy piston and it's sub 5 lbs with the sights/RDS and another that's almost exactly the same but isn't bufferless that's around 5 lbs 5 oz. You did well.