Qualcomm's was caught on tape at a "Born Mobile" (one of their own) conference in China, where he said Samsung's 8-core chip uses a meaningless number of cores, and that it becomes harder to manage the power consumption and thermal efficiency of such a multi-core chip, implying Exynos 5 Octa won't be very efficient.
I can't say I'm surprised Qualcomm is attacking Samsung's 8-core chip, because they have several reasons to do it. The reasons they are actually talking about, though, don't make much sense considering Samsung is not using a "normal" 8-core configuration, but a big.Little configuration, where the device uses either the low-end cluster of CPU cores or the high-end one, depending on its task. So there's nothing "more difficult to manage", because it acts just as a quad core, and it depends on the context, which of the quad core clusters it uses.
The real reason behind this attack are that if ARM's big.Little set-up actually works in delivering better battery life for devices overall, while packing even more performance than Qualcomm's own CPU's, then that puts Qualcomm in a pretty bad position. Qualcomm doesn't use big.Little, and I don't think they intend to use it anytime soon. I do believe they are using stand-alone Cortex A7 cores for low-end and mid-end devices (probably in the the S400 chip), but nothing in the big.Little configuration. If the market turns to such chips, then obviously Qualcomm is in a losing position.
If Samsung had actually made a regular 8-core chip, like the way AMD does them for high-end PC's and servers, then I would agree that 8 cores would be a waste, but it's only acting as a quad core, and I think quad core chips are necessary, at least for tablets, as they become more multi-tasking heavy. For smartphones, which have a much smaller battery, the use of quad cores is debatable, and their usefulness depends on what kind of applications we'll see in the future, that can take advantage of them.
Right now the browser and many 3D games do take advantage of them, but I think we need to see more "killer apps" that would be significantly slower without quad core chips in a smartphone, to really drive the point home for quad-core chips in low-energy smartphones. But Samsung is no "saint" here either, as they've been pushing for quad cores lately, too, and the S4 Pro isn't exactly a leader in energy efficiency. So they'll have to come out with a more credible message against big.Little if they actually want to hurt Samsung and their chip business.