Yes, it is. There is hyperbole on both sides of this debate. Being able to show we've made historic progress makes future potential progress look more realistic. It shows our institutions are capable of solving this problem.
I should amend my statement to say, "Is that a reasonable metric to use to declare success?" I regularly bump into folks who say, "Well, what more should we do? We're already better than we were 100 years ago."
Got it. I think there may be confusion between a metric and a threshold. The metric being certain objective measures of quality of life. The thresholds being where we were 100 years ago, where we are today, and where we should be today.
More broadly, anyone "declaring success" on such a broad question is--at best--deluded. More common is people throwing their hands up at what looks like an insurmountable problem. I've found pointing out the often-unappreciated magnitude of recent historical performance to be useful in that respect.
If you keep moving the goal posts, you'll never get there.
We can have major progress and still not have sufficient progress. We can make major improvements and still feel like we have a long way to go.
Just because we're better off than our grandparents doesn't erase that some of us are relatively badly off against today's standard, and we could be doing more to help those who are at the bottom of our socioeconomic ladder.