I like how they state clearly that the result they obtained, even though unexpected, does mean that there are things that we still do not know, not that all we know must be burned to the ground.
In some ways, this is exciting - deepening mysteries always provoking further study. But on the flip side, it also makes me ponder the thought that maybe we will never gain true knowledge of the universe. At least, probably not before a very long time passes.
Therefore, we might need to address the problem from the other end. This requires a totally different mindset. See for example the work done here: [1], or see the video lectures starting here: [2]
I think we might be excused to take a few more years to nail down the rest of gravitation. There's an embarrassment of riches of data; it just needs assembling into a picture.
If you are equating true knowledge with perfect knowledge, this obviously should be considered a straw-man. There is no reason why the rules completely describing universe should have to fit in a human mind. Our brains were evolved to solve the specific context of our prehistoric survival.
However, we will never truly grasp the outside World. Every discovery will open up another can of worms, in an endless chase for more refined models. Today it's Dark Energy and Dark Matter. Centuries from now our views will seem as naïve and simplistic as Phlogistics and 19th-century Ether.
That's OK though, as long as we're having fun. And don't blow ourselves up. And love and laugh.