Agoraphobic - remember, absorbing forces is part of what cowstails are for. Otherwise the ideal cowstail would be steel wire - which it ain't - rather than dynamic rope or tape with other force reduction features built in.
Even a very low stretch rope will possess some shock absorption value. This will be related to size of fall / length of rope available to absorb shock, so again fall factors do come into the picture. So you are quite correct to say that rigging may be an effective way of managing the risk of using this type of rope. Certainly, you'd be worse off if a main belay failed while you were just underneath it, or a rebelay failed if it was a short distance below a main belay, than if you were on a less static rope. This is why, when using spits, we double up the bolts and prussik sensibly in these circumstances.
Having said all this in it's favour, I've not used the black Marlowe for over fifteen years - just too heavy and bulky. Many of the long drops can be avoided by careful rigging and some effort and it's only rarely now that you get the 100m+ single hangs where it really comes into its own.
On a more cheery note - your average marine is certainly a wiry individual, but they'll probably be carrying more when they abseil than you do. Combat load used to be 35lb as I recall, plus a rifle; all of which makes both the dead weight, and the weight slung around the body, more likely to cause injury in the event of a fall; if the MOD accepts that the gear is good for those circumstances there is perhaps some safety margin built in. (Mind you, they have a higher acceptable casualty rate than most caving clubs - and operational abseiling has more alarming factors involved than high peak impact forces).
Anyway - you've got the rope. Don't sling it, just be aware of its limitations and use it accordingly.