I miss a lot of 'for me' or 'in my opinion' in your post. Because I can tell you it's not a fact, it's something subjective. A lot of people are not bored.
And to inform/educate you a bit more; there has been plenty of new blood added to the team. Because some of the original team moved onto Titan.
Plenty of new stuff and mechanics are being added with every release. before Firelands you never had a fight with mechanics like on Shannox, Rhyolith or Bethtilac.