This is simply not true, concerning 16 or 35 in 1950s, 1970s, or modern times. I'm not completely aware of the "standard" lengths that were used while shooting in enormous backlot sets or half-rooms constructed in warehouses, but those needs are considerably different than any faced by filmmakers, today.
For 16mm, generally, 25 is the longest lens in the Zeiss SS prime set, with a 50 being added later. Lengths are 9.5mm, 12mm, 16mm, 25mm, and sometimes 50mm (which is a specialty lens, really). Of course you'll get 8-64 canon zooms that put 25 in the middle, but it is not the standard length of 16. You also get 24-290mm Angineux Optimos for S35, but that doesn't make 125mm the standard length.
As for 35, 50mm is not the most used or most versatile length. At least not in the film industry, today, and apparently not in the film industry in the 50's, as Ozu was building sets to accommodate the length. The 35 Zeiss SS set was comprised of 18mm, 25mm, 35mm, 50mm, and 85mm lenses. General purpose is 30-40mm range.
And ever since people started masking their films to 1.85 or manufacturing 16x9 only sensors, the 50 has lost too much vertical information to remain usable as a near-standard length.
As for 8mm, I'm used to zooms, but the cameras aren't generally used for commercial filmmaking. And yes they do tend to run a little longer than 16, relatively (the classic 16mm Canon 8-64 is the same range as many high-end, but common, s8 cameras).
All that said, I'm not sure where you get your information. Location filmmaking has changed the game a little, and perhaps longer lengths were the norm is the Hollywood era. But 16mm is a modern format, and 25mm is not the standard length.