Amazon closes the listing a bit early to make sure they don’t oversell it, so they’ve released another ~20 recently and probably will release a few more in the next day or so as they ensure they have the stock.
Yeah the GG Two is lighter, but smaller, less durable (10D fabric, #3 zips), and less functional (singlewall, no vents, high cut fly etc). Good tent if you want something more on the lightweight fringe. Stratospire is the closest and also a nice well rounded tent (it’d be my 2nd choice). It uses more durable fabric than the X-Mid (30 vs 20D) but also ~6oz heavier, more expensive, non-seam taped, has struts to pack up, more complex pitch, and doesn’t use no-sag poly.
Another option is the SMD Haven but currently sold out out. Kinda like a doublewall GG Two. Weighs about the same as the X-Mid (2oz less but not seam sealed) but much smaller (44″ wide floor), more expensive, doesn’t use high end components like waterproof zippers, uses less durable #3 zips, and again doesn’t use no-sag poly.
Other options are Yama Swiftline 2P (but unavailable I think), and something from Lightheart Gear.