Were the "attacks" really unfair? He wasn't doing his job properly if he was just accepting the position of one group of lobbyists without understanding the technology he was regulating or the consequences of that legislation.
Also, I'm not sure what you mean by "entirely political", since surely criticism of politicians should be political (as opposed to personal), but assuming you mean "entirely partisan" (i.e. based solely on his party, rather than the policy itself) I disagree. Perhaps you can find some example of a Democrat using an embarrassingly bad analogy to explain something technical, but I suspect it would be met with ridicule too, especially if the analogy were being put forward to justify a bad policy.
Indeed, it wasn't really entirely political and unfair.
The Internet is a mesh of millions of computers that happen to be connected by wire or fiber optics or some other transmission medium. Fiber optic cables are the closest to "tubes" one could analogize, since it has a thing (light) being pushed through a cylindrical device, but it does a complete disservice to the technological advancements to dumb the whole of the Internet down to "series of tubes".
The attacks on Stephens were very justified in that as a leader of the committee, he should have been much more well-versed in the actual technologies used. He should have wanted to be more well-versed. And if lobbyists had that much pull and sway over him and what he "knows" and how he presents it, then the ridicule was even more justified.
You can try to sugar coat his ineptitude all you like with a plethora of excuses, but, in my opinion, he got what he deserved with the ridicule.
OK, I'll bite: tubes/pipes/flow is a bad analogy for packet-based network transmission.
Overall though, it doesn't make sense to argue the required corrections of this statement unless you also think a good analogy for a simple circuit is "wires are straws through which electricity pours".
But an important part of demonstrating you're worthy of legislating the internet is talking the talk - demonstrating you know how what the industry is and how the industry operates. A suitable replacement statement which demonstrates a command of the basic ideas would be:
"If we exceed the capacity of our internet backbones, critical services -- as well as consumer services -- will be impacted."
For me, "tubes" was less of a gaffe than referring to an email as an "Internet". The former was a bad metaphor, the latter was a failure of basic layman terminology. It means either you don't know what you're talking about, or you're a bad communicator, and either of those should be disqualifying of your post as the head of a senate committee on internet legislation.
The attacks on Stephens for this were entirely political and unfair. He certainly was awful, but the ante-twitter mob that converged on him led by late night comedians were computer illiterates parroting what they heard.
The reason he said it that way is because he was an old corrupt coot who had net neutrality explained to him in very simple terms by lobbyists and PR flacks trying (successfully) to stop it. The reason he was taunted over it was because of a strategy come up with by the opposing PR flacks, probably gathered around the same brand of whiteboard.