I guess the parallels between HE and Friends are obvious only to me and the writers of HE, who included a "shout-out" to Friends in one episode, by referencing the parallels - Dave = Ross, Alex = Rachel, Max = Fat Joey, Penny = Phoebe, Monica = Jane, and Brad = Chandler.
^^ The point I was trying to make was that both shows owe more to Seinfeld than H.E. owes to Friends. In other words, there may still have been a Happy Endings without Friends and vice versa, but neither would exist without Seinfeld. So it's kind of irrelevant that H.E. looks a little like Friends structurally -- that's only natural, since the two shows had the same parent.
So Seinfeld is responsible for the fact that both shows had 6 characters, and both shows had all six characters develop parallel relationships? That's a stretch if you ask me. HE didn't need to have two characters married, two as exes, two as siblings, and two as ditzes.
Character-wise, as in the choice of having 6 characters, two of which are married, aside, the tone of the show more matched Scrubs in my opinion than Friends. As far as the creators of Happy Endings and their thoughts on how it is or isn't like Friends, I'll defer to David Caspe: Source.
Happy Endings took place in "Chicago" though. Anyways, I'll miss this show. The number of jokes they crammed into 22 minutes was crazy.
The similarity is in the structure of the show, ensemble acting concept with multiple storylines for the characters unfolding simultaneously. The "show about nothing" concept is also a Seinfeld thing -- the characters carrying on and exaggerating their reactions to relatively trivial matters to a comedic result. Friends borrowed heavily from the basic Seinfeld (and so did H.E.) formula but added romance which was really just a superficial embellishment. I wondered where they were supposed to be. Wait, was the show shot in Chicago or was that where the show was set? I used to have to regularly roll back the DVR to catch all of them. That cast spoke faster than any ensemble I'v ever seen or heard.