Roman Heavy Cavalry Fighting Techniques

[Kai]

You can ride perfectly without them, and I don't see why they should be 'crucial'. In my opinion Junkelmann adds to much weight to his 'see, I can ride without stirrups, isn't that nice' debate.

I am sorry to be blunt, but I feel this is an incorrect summary of Junkelmann’s positions since most of the pages devoted to the riding without stirrup (pp. 104-120 in Reiter Roms, III) tell how useless the stirrup in most situations is – with one notable exception, which I think is important in melee (I’ll try to translate the section):

"The one advantage offered by stirrups in combat is that the rider can fully erect himself when necessary. This makes it easier to turning (your body) to the sides or to the back in order to slash, thrust, or shoot with the bow. Although this is possible without stirrups to a certain extent, it needs more power/strength and flexibility in the hips. Moreover you can stand and put your weight on the inner stirrup thus keeping your balance easily when turning quickly as it is necessary in melee. The rider without stirrups meanwhile has to grip to the horse with his thighs and balance himself by pressuring the outer thigh on the horns of the saddle (if available), both of which is quite tiring." (p.111)

Now imagine that with one lightly or unarmoured rider, and one having to bear more than 25kg of armour or more. Again, it is not so much about riding as it is about the ability to lean and strike to the sides, to turn around, and to turn in your saddle. Here the stirrups are useful, especially when wearing lots of armour.
We classicists are quick to believe medieval people were stupid, but they were not. They had good reasons using stirrups for their heavy armoured cavalry.

But on your other points I fully agree.