I've seen two discs very clearly that were neither balloons, nor exhibited visible means of propulsion that would explain their performance.
I'm not saying they're ETs, secret projects, interdimensionals/demons, or whatever, I have no idea what they are.
However, as to your question "how these ultra sophisticated crafts travel light years through space yet crash on earth like a Cessna 172." Answer: They didn't. Not the little discs flitting about the atmosphere and near Earth orbit anyway. The beings - or AI. - who created them may have arrived millennia ago in what we would call a von Neumann probe, and assembled their local shuttles for local use.
The AI built and piloted von Neumann probes could be part of an advanced civilization's much larger diaspora, and could take their sweet time going from source to target and would not violate Einstein's speed limit. If this civilization was a hundred thousand years more advanced, it could have already colonized a good chunk of our galaxy's neighborhood.
Good post—aliens would be foolish to risk exposure to hostile planets when they could have probes/AI/robots do the heavy lifting of initial exploration.