ED and NMS are different games but still it leaves me gutted to see what a small team like Hello Games pulles off in such short time in comparison to what the much much larger Fdev has achieved in what four five years?
That's probably because you (and me) don't know what goes on behind closed doors. Same goes for CIG/SC (despite their claims to most open development ever, we don't really get to see what goes on inside).
We understand FD to have around 100 people working on ED. HG has a lot less. It would be a bold claim to try and say that the devs on one team are better than the devs on the other. On average, they are probably equally skilled.
So, if FD has more people, and equally skilled devs, its probably because FD are doing stuff that is either more complex and taking longer (which is definitely the case in terms of planetary generation) or there are management issues that result in the devs being less efficient in terms of productivity.... but like with the devs, it would be a bit of a bold claim to suggest that HGs management are more compoetent than FDs.
One advantage HG probably does have is they are smaller, which means they probably have less internal beauracracy, so when Sean says "I want X" his devs can just dive into it without excessive meetings and design documentation, etc.
But, without insider information, its near impossible to know the reasons, all we have to go off is what is actually produced.