I have concerns. Darnold had a really good supporting cast in Minnesota, with multiple good receivers, a reliable RB, and a good OL...plus a defense that was good enough to keep opponents to a reasonable score. It was a good situation to be in, and expectations were pretty low because he was supposed to be the backup. Everything will be different in Seattle - he has no OL, his RBs are unreliable, and right now he's got one receiver. And....he's the guy.
On the plus side, I don't think Geno was ever the answer, and I assume that they're saving a little money on Darnold - at least for this year. They bought a little flexibility and some time, and can now focus elsewhere. If Darnold pans out, great...it was a good move. If he doesn't...there's been little harm done, they needed to address QB anyway, and they have a placeholder for now. They can build up other areas and then find a new QB...which they needed to do anyway.
That said...the trend toward paying a QB based on 1 season of success is disturbing. QBs who look good on a solid team that makes a deep playoff run are not necessarily the same guys who are going to look good on a bottom half team. They're the ones that get propped up by the people around them, but can't carry the people around them. Nick Foles is another great example.