A single staircase could be an issue with bigger buildings, but in the case of the one shown from Prague, there isn't even really a way to do two staircases, unless you have an outside fire escape like they used to do back in the day. Personally I'd rather take an outside fire escape over an interior staircase in case of a fire.
In places that have this single stair approach to low and mid-rises, it's often that the fire truck is considered the "emergency stairs" either out a window or off a balcony. Countries then add the multiple stair requirements and other safety rules when a fire truck can no longer reach the unit (typically over 5 or 6 floors).
Single stairs v. our 5/1 or interior corridor designs aren't a panacea that solves all problems, but there's logic to explore designs like these as our current approach has limitations too. There's
little evidence North American buildings are any safer in fires despite having typically more stairs and interior hallways, but plenty of evidence that interior hallways and less efficient floorplates tend to make larger family-sized units impractical or with lack of windows. In part, these design choices limit affordability and diversity in unit type within low and mid-rise apartments.
A critical part for these complex housing, design, affordability issues to remember - the status quo isn't "free". Many of these standards and design conventions we have today have costs that we can't see because we are used to it. Each of these standards and design conventions may have good rationales in isolation, but together combine to produce less efficient, less livable and less affordable outcomes on a whole. Lots of these rules aren't easily reformed either as there is such low transparency into how they were decided, no clear publicly-visible process on how they can be changed, and myopic siloed thinking by the defenders that "own the rules" in specific issues that tends to reject challenges to the status quo.
It's taken 20 years of advocacy to daylight the pseudo-science and stupidity that is how we decide parking regulations in North America to
finally start to move the needle in parking policy. Another classic example is fire truck-defined street widths where the policy in many cities was to make wider streets on the theory to get trucks to emergencies faster, but with
limited evidence that street width is the critical factor in response times. The result was "safety" standards that for decades produced wider and more dangerous streets, leading to more pedestrian fatalities, ugly neighbourhoods that cost more, and new storm water issues due to all the extra pavement.
Both the issues above are being challenged here and elsewhere, to better - if painfully slow sometimes - outcomes. Perhaps things like stairways and fire codes could use a little of that same scrutiny.
