The thing is, a lot has happened since 2016 -- and why *shouldn't* I complain about it, since it's mostly been a confused and messy attempt to rush through something without anything even remotely resembling proper planning.
Rather than rushing, as you seem to think was necessary (but, as I've said, would have been illegal!), the government needed a proper plan for as many contingencies as possible. They didn't achieve that; it's not clear that they even tried.
Also the 2017 snap election was a rather stupid decision that has backfired spectacularly, and has left us with a leadership that can't even organise a proper rebellion. All of this is just harming the UK -- I don't think anyone can honestly believe that taking time to implement the decision sensibly and effectively would have been the worse path, as opposed to this chaos.