There are a few quests you can miss catching early on, but not 5 hours worth. The playstyle difference would be a large part of it. I quickloaded quite a few times to maintain perfect stealth in some quests. I played similarly in DX, HR and MD, and had about 23 hours for the original, 21 for HR and 20 for MD. HowLongToBeat reports that the original game is around ~24 hours for main story on average, HR is 21, and MD is 14.5. However, the "Main story + extras" and "completionist" runs show them all to be much more even on aggregate.
I think it is the shortest, but there definitely wasn't an entire half a game cut. The only significant villain we've come across in the story who didn't get dealt with is Bob Paige, who can't be touched for obvious reasons. The main dangling threads are - what the fuck was the deal with the aug clinic / mystery aug plotline, and who is Janus? While still laving those questions, neither feels like enough to base a whole game around, or even half a game. More like an hour or two of extra content.
Prague itself was very expansive and had a lot of care put into it. I would have preferred a smaller Prague with a second hub in some other part of the world, but also kind of see what they were going for, where we experience it in three phases, day, night, and after lockdown. The real sin, though, was how frequently the game forced you to move between load screens to complete sidequests. I had it on SSD so the load times weren't bad, but sneaking in and out of train stations under lockdown was