Absolutely brilliant and unique!

...add something different than the static and stone-like horses. ...
Those have always irked me as well. They're (sort of) fine when standing on their own, with a rider on top, and could even work as part of a larger formation trotting just before the charge. But for things like this, a pulling pose, like a draft horse would be so much better.
Something like this:

I get that at the time they had to make do with the sprues they had available; plastic moulding was initially extremely expensive, and they had to get as much mileage out of each one as they could. But some heavily built draft horses, pulling a large weight would be so much better.
Are there manufacturers who make horses like that at all? In 28mm heroic I mean; I'm sure there are plenty of 20mm and 25mm historical horses that fit the criterium, but they'd be too slight for something like this...