However, I think you are all missing the OPs point a little bit. Sure, you can make the game harder by doing Lone Wolf or trying to solo or something. But the OP is in the middle of the game. He presumably does not have Lone Wolf, so that's not an option yet. And besides, someone should be able to play with a full party (which allows the most fun options and strategy) and not have it be too easy.
I do not think we are missing his point. There is no official harder difficulty. They certainly might create an even harder difficulty in the future, but right now the only options are to challenge yourself with limitations. Which, to be fair, is a tried and true method for people seeking greater challenges since video games were invented.
So it is perfectly reasonable to suggest alternative methods of playing that would make the game more challenging. The tongue in cheek is just for humor. At least I didn't pun.