Stefan,
The reality is that it always depends, everything is a matter of tradeoff, once you step over the fallacies.
So again, Isomorphic Javascript seemed to be a distant dream, SAM makes it absolutely trivial to move elements of the pattern (Actions, Model and State) between the client and the server, at any point of the implementation (that’s probably what you seem bitter about because you see how powerful an argument it makes). Please note that this is not a binary choice and as little as a single action can be moved to the server.
It’s easy to debunk the arguments behind this article:
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the Web server can only be written in Javascript: most organizations would see this as a big plus as developers can move (nearly) freely between Front-End, Back-End, not to mention Integration if you see something like Node as a terrific middleware.
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“Client-side javascript has access to an in-memory state machine that allows for a fine-grained level of interaction, with a very low latency (sub-milliseconds). The same in not true for the HTTP state machine, which is driven by link clicks and form submissions.”: this is possibly the biggest fallacy in the argument against Isomorphic Javascript since for most (business) applications each user event will translate into some form of API call. Who could argue that the HTTP state machine is not prevalent in Front-End architecture. I would argue even further that trying to ignore that simple fact like most Web frameworks do, is a major faux-pas, and the source of major pain and aches when developers need to stitch together pristine Web frameworks with API calls.
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“Blocking vs non-blocking data flow”: obviously this guy has not heard of Websocket
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“The infrastructure then needs a way to make sure the smart leaf’s context doesn’t get lost”: obviously this guy has never heard of single state tree architecture, and the SAM pattern in particular.
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“Mobile devices freeze during parsing of javascript” not much to add here
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“Isomorphic Web Apps is an approach that demands a high level of development skill.”, with SAM the additional skillset is exactly zero.
etc! Benchmarks can help. I have not been seeking long, but here is an example (2011, quite old): 
especially for F50 :)?