These are really, REALLY poor excuses since they have been pulling off longer seasons for years now with no hitch. Maybe (and we aren't sure yet) they will have a few more battle scenes but the shorter seasons were supposedly one of the reasons for that.
The creators can do whatever they want. If it takes two years to make a season, then I and the rest of the world will wait two years. What does it matter? It's the most popular show on television right now despite some recent dips. I'm sure they want to stick the landing. A little more time in the writer's room, a longer production schedule, more time spent on special effects -- these things are bad to you?
I'll never understand why people get so upset at delays. There are so many excellent shows, movies, books, and video games out there, I have no problem waiting a little longer for the creators to achieve their vision.
It should also be noted that I am a huge fan of A Song of Ice and Fire. Clearly, I have no problem waiting for sequelsl. A Dance With Dragons came out six (6!) years ago next month. But I'll wait twice as long for The Winds of Winter if it's as good as the first five books.