I completely agree with you on this point. Also if a set is produced far too big to be placed alongside other contempary sets from the same or other manufacturers it is a real shame and does not help the hobby. I don´t think that the various manufacturers realise that producing the figurs all to the same size would actually boost sales. When Ceasar produced their first box of Ancient Egyptians they were in 1/72nd scale but obviously shorter than the Atlantic figures. However, they went on to produce more than a dozen further sets for the Bronze Age Chariot Warfare period, so that when Zvedza produced their 26mm giants I only bought 1 box. If they had been in scale with the Ceasar products I would have bought multiple boxes.
Now with my beloved Mid eighteenth Century (SYW AWI) the figures range from 23mm to 26mm and can not be used alongside each other. This is a real pity when by the use of Head Swops I can increase the variety of troop types. On the correct end of 1/72nd scale I have British Light Dragoons made from using Revell SYW Austrian Dragoon Bodies with heavily converted Airfix French Imperial Guard Grenadier Heads Mounted on Airfix French Cuirassier Horses (the ones with the French saddles), after completing this conversion Italeri released a set of 26mm British Light Dragoons that tower over their Infantry comrades and their sister regiment.