Hi devoidapop,
Yes I did indeed review this tent for Trailspace.com in 2015: http://www.trailspace.com/gear/msr/flylite/#review33314
Not to besmirch outdoorgearlabs (whom I think highly of) or Backpacker Magazine, but I think my review is the most in-depth you'll find and you're right: from the pictures I saw it appeared that OGL didn't pitch it taut for whatever reason.
I think my review sample was a pre-production prototype so it's possible there have been some changes since then. I believe my review will answer most of your questions, but I can answer these directly:
Did you keep the mini pegs or go with something larger? Those mini pegs were wholly inadequate for me. That design catches wind like a sail, the single foot-end stake is critical, use a good strong anchor at that spot.
Any success at creating a vestibule with a poncho or raincoat? I didn't really try that but did use an umbrella as a porch a couple times when the weather allowed it.
Did you feel like it needed a rainfly in heavy rain? Indeed this tent did not do well in any extreme weather.
Was the floor too thin to not use a ground sheet? I didn't use a ground sheet, seemed fine without.
In the right conditions this tent could be OK. I'm thinking of arid places in the western US where humidity is not a factor. In the balmy southeast this tent is a condensation factory when you close the door.