Was the leather muscled curiass of the later times sexier?

[Tarbicus]

In the Crimea the Russians' thick woollen greatcoats were sufficient to stop many British cavalry sabres cutting with effect, non-metallic armour is not entirely despicable.

Which has nothing to do with this discussion - those coats were felt which is more than attested to as very capable armour. Normal everyday leather is a completely different story.

(edited - see rawhide comments below)

Why couldn't those supposedly flexible musculatae be felt?