I think the criticism is actually fair; it's stupid to always quote humans saying "Xchryxchub" when they're actually saying "Krikoob," as that implies they're better at pronouncing the weird alien name than they really are. Going to the trouble of inventing an orthography for their weird alien language in our alphabet, and then disregarding it, is part of the superfluous exotica complaint that Orson Scott Card levelled (and in the fantasy department, I believe Diana Wynne Jones has said something similar.) For that matter, maybe "Krikoob" should be spelled "Crickube"—a completely natural English spelling, but nothing disappointingly baby-ish.
There's an exception, of course: eventually the weird orthography would become legitimate if the two cultures remained in contact long enough and the aliens were thoroughly studied by our linguists. The onus is then on the author, like any explorer describing a newly-discovered civilization, to document and explain the correct pronunciation as best he or she can. (And if that gets tedious, perhaps a civilization with thirty different velar plosives isn't really appropriate for writing stories about. Much like diarrhea, comparative shopping, and trying to get ketchup stains out of a casual shirt, not everything makes good reading material.)
That's more a product of an inappropriate choice of orthography. I'd be willing to bet his non-English readership was somewhat better at getting the names right, as would those with a Classics education (and given the age of his writings, much of his initial fanbase would've had such.) When a real constructed language is used, the problem of conveying the correct pronunciation becomes hilariously complex, since the orthography has to be internally consistent more than it has to be transparent to the reader.
Still, there are ways authors can provide cues—have characters mispronounce the name ("Leg-o-laz?" asked Frodo. "No, it's more like Le-go-lass," said Gimli. "I wish I could actually hear you saying that instead of just having to read it on the page," whined Pippin. "This example isn't really going where it was supposed to," said Gandalf.) or use an alternative orthography when English speakers use the name in an English context.
I had a somewhat longer post prepared originally, which was essentially a complaint about how no one ever seems to go the imperialist route for naming and call things Betelgeusian (notable exceptions: Martians and Terrans.)
The natural thing for two cultures in contact, at least up until the later half of the 20th century, was for words to be assimilated more fully. The silly letters get massaged into something more legible, and sometimes even calqued or translated. Hence for hundreds of years we had "Canton" instead of "Guangdong" for a certain Chinese province. Still unfamiliar, but not rawly alien.
In my opinion it would make more sense if we saw more of these compromises, particularly for far-future settings where lots of contact would've been standard. Eventually new words, no matter how alien, get assimilated.
For what it's worth, from TFA:
While 75 percent of students in 2012 said, before Mumper’s class, that they preferred lectures, almost 90 percent of students said they preferred the flipped model after the class.
So it looks like the backlash is relatively minor.
e-credibility: the non-guaranteeable likelihood that the electronic data you're seeing is genuine rather than somebody's made-up crap. - Karl Lehenbauer