Granada is one of those which is an endearing garden piece. If not for its history, then for its many unique features which still hold steadfast even today. I've found Granada to be one which will always hold a place in my collection, and definitely keeps up with many of today's incarnations, if the conditions and situations are suitable,
I read about other's failures and issues, and all I can say is that it must be some other reason why the failure. Surely, it cannot be because of just humidity or rain. I grow 100% no-spray. Our humidity average is about 70% year-round. Our average rainfall tops most all mainland states at around 120" annually. Some days, we can receive up to 4 inches within 12 hours.
There could be one huge difference. I grow all my roses Own Root. Including Granada. I'm fairly certain that many crosses which do terribly could become an entirely different plant when grown on their own roots. Whatever crosses struggle too much on their own, I allow to die out, I note the issue, and never grow that again.
I truly believe soil prep and appropriate location is absolutely key as well. Kim has mentioned this before, and I wholeheartedly agree. While a budgraft is easy to find and plant, I've observed two entirely different end results (which overwhelmingly are highly favorable) when grown Own Root. I believe Granada is certainly one which shouldn't be grown on a graft. It has amazing vigor, stronger fragrance, and even resists all of the usuals, like rust and mildew. Also, the Own Root subject which is a mere 6 feet from the Grafted parent does not get affected by black spot at all. The grafted subject usually loses all of it's lower foliage and is half naked by October. Not so with the Own Root clone.
My observations have led me to understand that when soil and roots collide, there must be enough of the correct elements: Aeration, WATER, Micronutrients, pH corrected, and above all.. Correct density of the soil.
I also observe that some love to grow on hillsides (for example). Others detest it. Some love to grow along side a tree. Others die from that. So, my best hypothesis to this rose and all others which I've tested environmentally, is that one size certainly doesn't fit all when it comes to planting a rose :)