As others have noted the newer atoms aren't the same as the old under powered garbage. I've actually got a server running one of the new Atom server chips. It's a good low power processor with some strong capabilities for the power envelope it uses.
Though there is one exception, there are some under powered Atom chips. They are smaller and use even less power and generally aren't intended for a PC type install. But they do exist because Intel is still trying to figure out how to sell chips in this space without totally cannibalizing desktop sales with chips they lose money on.
Which chip Microsoft chose (or whatever one Intel let them use) is going to determine whether the surface 3 is garbage or a reasonable balance of CPU and power use. It's entirely possible it's going to be way to slow for use in anything CPU intensive because Intel is still making Atoms that aren't very good, even if they are better than the previous Atoms.
It's interesting to me that Microsoft isn't saying WHICH Atom they used.