You might be even more irked when you perceive the 'variscale' that is the accepted norm for HO steam models.
OO was born out of the necessity to accommodate commercial mechanism parts within the limitations imposed by the UK loading gauge and UK steam locomotive design, most critically the close fitting splashers over driving wheels and the outside cylinders and rods and other components in close proximity to these. The compromise is a constant larger scale, excepting the track gauge.
HO shares the problem of accommodation of the same commercial mechanism parts on steam locos. Even with a larger loading gauge, the larger locos in particular are difficult to produce as working models able to negotiate small radius model railway curves, and the accepted compromise is to move toward 4mm/ft (OO scale) for width around the mechanism. Lima attempted an LMS Crab, and Rivarossi an LMS Royal Scot, and effect is noticeable, as in ugly.
Occasional Japanese and Korean HO brass productions as mentioned above are typically true scale, and the outside cylinder types require scale minimum curve radii, in excess of 1m. Where this all leads if you are sufficiently irked is P4 - true 4mm scale - or P87 - true 3.5mm scale.
