I agree with OP, take that crap outta here. It's simply inaccurate.
For starters, the original TV series (or first two movies) did NOT have a happy ending. Madoka sacrified herself, sure. but what do we see right afterward? The world is 99.99999% the same as it was before her sacrifice. QB is still there contracting girls. The girls still fight–only it's "wraiths" now instead of witches. And in the Japanese the names of those opponents are even more similar than they are in English: Majuu (wraith) instead of Majou (witch). The ending of the original is very much about futility, just like many points earlier in the program.
2) Homura's change to Homucifer is also perfectly in line with the recurring themes of "balance" and "fate" in the TV series. Throughout the TV it is stressed over and over again that the world is always in balance. So if Madoka ascends and becomes a god-like figure (Madokami, Ultimate Madoka, whatever you want to call her) it is expected that there will be some kind of balancing force as well. And that's Homucifer.
Whoever wrote that is free to not like Rebellion. That's perfectly fine. But that snippet of text shows that the writer seems blind to the events of the TV. Thinking that PMMM has a happy ending is just as silly as claiming that Eva is a show about giant robots. It misses the point completely.