Simplistically speaking: Companies fail because of two reasons (1) Users dont want what they make. Examples are Kodak and Nokia. At some point users wanted what they made but at some point they stopped wanting it. (2) Users still want what the company makes, but there is no profit in making it. Example is Dell.
Obviously we all know the role of competition, monopoly, commoditization and branding in (2). As in any maturing products, margins in Phones will fall. FruitCo does not make as much money in the iPad mini as they do in the iPad. And iPad mini is cannibalizing iPad. There is pressure on FruitCo to further lower prices on tablets and phones. As long as products are interchangeable, there will always be pricing pressure. UX has no role in this. Making a million types of products, if done in a sane way has no role in this. Sure you can argue that UX ultimately contributes to brand image which in turn contributes to users willing to pay more -- but that connection is tenuous at best. Good customer service and return policy will also get you brand loyalty, despite shitty usability. You can verify this point with Amazon and their website.
The biggest danger to companies is from (1). And that typically happens when products with game changing capabilities are introduced. Sure you can lump them into UX -- as in "I can do more things with it, so my user experience is better" and lump it with "product is light, small, has premium feel and winds smoothly. so it has a good UX" --- but that gives no insight.
If I were in Kodak at that time and asked "how can I improve the UX", the answer would be smaller film, easier loading and unloading of cartridge and easier processing because the camera recorded the shooting conditions into the film. Kodak in fact improved their UX and came out with ....
Advanced photo system film cartridge!! . A boatload of good it did them. The irony though was that Kodak made the first digital camera in 1975, but never took it seriously. Nikon had several film camera models, at every pricepoint. That doesnt seem to have deterred them from moving to digital!
Game changing capabilities is what killed Kodak, not smoother cameras with better construction. Digital could shoot many photos, seeing them instantly and reshooting if necessary, zero cost of shooting pictures....
One way of getting game changing capabilities is to make your platform programmable. Programmable platforms always win, because use cases that nobody dreamed of while making the products can be enabled. Think of what would have happened if Mahdi had his way and iPhone was not programmable (at first he refused to release a SDK). It would have been a no-contest with Android, it would have killed the iPhone dead in no time! Nokia was blindsided by this, they were competing against a programmable platform with thousands of apps. Thats why "burning platform" memo was written and it wasnt titled "Need more glass", "need less seams" or "make scrolling smooth"
Yes premium feel and smoother scrolling matters, but it is not even two orders of magnitude near to how important capabilities are. The point is, can Sammy spot the next game changing opportunity and jump on it. You argue that a big product portfolio distracts from making tight seams. Well there is some merit to it. You argue that a big product portfolio distracts from spotting the next game changer. I am not so sure about that.
Point is, sammy may or may not get blindsided. But one data point is that Sammy is still investing in R&D in processors, flash, display tech and battery tech. This is not a mark of a company that is complacent about looking for the next game changer.