Great review Gis, I really enjoy your understated humor, and agree with so much that you say.
One thing you might have missed, if the symbol is a black lion (I think maybe it's actually a leopard or puma as it lacks a mane), why is the helmet crest red? It should be BLACK, for goodness sake.
Playmo have a horror of monotone. They just seem incapable of producing a single color knight. The main man in full plate should have the plate legs, but the tops should be silver not black. With the legs they gave him, if the boots were silver to match that'd be OK. He should also be on the horse (with full caparison), and the lesser armored man act as his squire.
I don't mind the helmetless figure, I've got tons of spare helmets and hair if I want to switch, and as he's a long way from the action, he may have chosen not to wear a hot and heavy helmet, or as Eric said, maybe he just couldn't afford a helmet.
As to the cannon, gunpowder was recorded in England in 1334, during the reign of Edward III, so there's plenty of opportunity for an early cannon like this one, though what on earth that missile is supposed to represent is another matter.
The castles in the series have no round towers, and were clearly not built with gunpowder weapons in mind. That's OK too, because obviously you don't develop a defense against a weapon before you've encountered it, nor are castles rebuilt quickly.
As the basic army-buildign set in the series I'll be buying several whern the hit the US, though as you say, there are a few modifications required to the figures to make them more acceptable. As Bolingbroke and Eric observed, you'd think the designers could do a better job than we could, but they obstinately refuse to.