Well, it's not hard to hate Samsung products. Besides, he isn't the only one that hates them. Look at my posts from earlier in this thread; I also hold a strong distaste for Samsung products because of TouchWiz. I just don't talk about it much.
Edit: I still don't don't see the hate for large phones, but we all like different things. I really like my 6P *shrugs*
I don't like how they abandon their hardware so quickly. It's like well they made fancy exclusive proprietary hardware that uses proprietary drivers.
The problem is Linux's nature with kernels and drivers. A bump up in the kernel can simply destroy drivers, causing delays in already an arduous process of carrier approval. Driver approval. Carrier approval. So many sign-offs.
That thing with security updates? That's the Linux kernel if you didn't know already. You can always track progress here: http://www.kernel.org/ Of course, Android kernel is slightly tinkered with its own additions: http://www.linuxfoundation.org/news-media/blogs/browse/2013/03/defining-android-vs-embedded-linux
Short-sighted companies don't consider maintenance as part of the initial costs since that drives away profit. Samsung ruined Android in that aspect. When sales department decides product portfolios without consulting engineering supervision, backfires will happen.
One-handed use and pocket-factors are still important factors to consider. Every user has different sized hands, so those factors matter.