To feel justified in thinking the universe is "essentially" understood is to be OK with one's concept of the "essential nature" of the universe to be inherently divergent from a future concept, which according to Asimov's own argument is going to be more correct than our own.
To me, it reads as a bitterness towards mortality, a sort of sour grapes: the insights we will have about the universe at some future time must not be very interesting compared to what we know now, because I won't be around to know them.
edit: I guess I shouldn't be surprised that Asimov's perspective is shared here. It's very easy to understand the essential nature of the universe when you define the universe as the parts you understand.
I don't think human beings in 1000 years will look at our current understanding as special in any way. As transformative as our era is, it will be dwarfed by the scale of transformation in future eras. It's just the most transformative era so far. That's temporal bias, nothing more.