It makes what Tatum did all the more impressive.
Don't think it says all that much about the rest of the roster.
As for how do you challenge the Nets?
You need a team that defends the three super well, that can handle isolation matchups without fouling, and on the other end I think you need to physically punish Kyrie / Durant by making them fight through screens and trying to get them into foul trouble with drives, post-ups etc.
You're never going to outgun the Nets, but you need enough firepower to keep up and occasionally have bursts of scoring to close gaps or build leads.
Finding ways to pick on Kyrie, Blake, and Joe Harris seems important, as well.
I would also say that you need to be able to play a slower paced half-court game, because if you get out running that's playing into the Nets hands. You need to force the Nets to rely almost exclusively on outside jumpers and then hope they go cold.
Overall, the Nets' crappy defense should be their vulnerability, apart from the health of their main guys. So far nobody has been able to truly punish them for it.