" They were clearly either cowboys or just incompetent as there would be
no way for trapped moisture to escape thus accelerating the decay ... I
would imagine that pebbledash would be effected in a similar way.

Providing a coating adheres to the surface, and is in itself waterproof, no
moisture should get in in the first place. This is near impossible to
achieve with render because invariably there is a gap between it and the
wall

If you can find the source of the penetrating damp (gutters, down pipes,
gullies, roof tiles etc etc) it might be simple to eliminate it rather
than the symptom.

Penetrating damp is usually just rain hitting a porous wall. You're lucky if
there's an obvious source. If the wall is already painted, or you can bear
to make it so, solvent based masonry paints are very effective IME