Reluctant rhododendron

Don’t think our rhododendrons like our sandy-clayey soil much – or maybe the bugs are getting to them. Either way, they don't bear much resemblance to the extravagant blooms I remember from my childhood. Maybe they’ll get a grip in time (come to think of it, I was amazed at how they have taken over by the river in the Doone Valley, in Devon. Where's the heather and sheep-cropped grass that I remember)?