Those are valid points, and they all apply to Samsung's DeX too, just on a larger scale.
HP's move is smart, too, because as many critics have pointed out in the past, what regular consumer would want or need Continuum today? The technology is expensive, a bit clunky, and slow, especially compared to a laptop or tablet that users already likely own. Those are safe bets for HP due to no expenditure needed for consumer advertising and stocking store shelves. Nonetheless, companies such as HP see real value in the idea - even if it's not fully realized today - for enterprise and specific professional markets where security and management are valued. Microsoft's Continuum always seemed like a neat concept, but even with the Creators Update, it is best described as half-baked. We're still years from that idea as pricing needs to come down, but it is not clear that middle- and upper-class consumers are the most viable target for Continuum or DeX in 2017. Keep in mind, Microsoft's long-term vision of Continuum is for emerging markets where many people will never have a decked-out Core i7 desktop PC. And that's not even including the "spare" display monitor needed. The point here is not that Elite x3 is some value proposition, but that at $900 (plus tax) Samsung's S8 and DeX are not priced for your average consumer.
Samsung did not announce the pricing and availability of its desk dock, but some earlier reports pegged it at $150 (it also has a fan to cool things down, which is interesting what happens with a wireless connection, if possible?).
In comparison, the Samsung Galaxy S8 retails for $750 with no desk dock, and the S8 Plus is $100 more.