The sets you mention Flambeau do indeed have poor horses so you are correct.
I wasnt impressed with the Italeri Prussian & French light cavalry sets overall anyway. The Prussian dragoons are giants with odd poses and postures. The French set had the same problem as the infantry set.....rather chunky, well fed, fellows who seem to have lost their necks and chins!!
Mars i dont think ive ever bothered with and im not a fan of the Airfix Cuirassiers as they just didnt seem to have the "presence" of heavy cavalry to me anyway.
I think in relation to Strelets horses,it is not that they are the worst horses ever made, instead its that they are indeed poor....AND being reused again in other Napoleonic sets, so it will be a recurring problem. Strelets can do much better I think, which in a way is a complement to them and how far they have come.