You've deliberately recreated someone's work with the intention of offering a competing product. Legalities aside, it's pretty damn rude. Yes, it's a rip-off. (I don't use that phrase lightly and I'm usually all for remixing, which this isn't.)
No, he is correct and you are wrong. "Original", as used here, is a term of art that means "not infringing anyone's copyright". Like it or not, "look and feel" has not been established to be copyrightable. Just ask Apple: https://en.wikipedia.org/wiki/Apple_Computer,_Inc._v._Micros...
I'm wondering how is this very different from MS Office vs. LibreOffice...
Granted, latest incarnations of MS's products are a bit different with the (crappy) ribbon and all, but LO is quite similar to previous versions of Office.
And I'm talking both about UI, design and functionality. Think Excel/Calc functions, for example.
If you copied the articles, yes. If you copied the design using none of their assets or code, no. Copying it definitely is, stealing it definitely isn't (at least not in the legal sense, the moral sense is debatable.)
You should have confidence that you will win because you can implement it better, understand the need better, can craft better solutions faster, and have better content on your network. If those things aren't true and all you had was an idea, unfortunately this was bound to happen.
Ideas alone are not defensible, practically or even legally. Successful implementations thereof can be however.
As I stated in my post, I'll be changing my personal design shortly.