If the time travelers go on public transportation in NYC or Boston, they see perhaps worse technology than they had 70 years ago.
Airports work less well than 70 years ago, though air travel prices have decreased.
Our diets work less well than 70 years ago. Agricultural and nutrition science have not materialized any benefits for the public w.r.t. obesity or diabetes. Though we have more life-saving tech. Diabetics live much better, but we have vastly more of them. (~10% of the USA is diabetic. CDC report in 2017: More than 100 million Americans have diabetes or prediabetes)
Building a new house is more complicated and expensive per foot than 70 years ago. Though insulation is better.
High trust societies work less well than 70 years ago. Trust is a resource, slowly renewable, and many places seem to have squandered it. There are a lot of such social technologies that have been working less well over time, I imagine. We may(?) now have fewer pleasant, human-scale built environments than existed in the 1950's. A huge obstacle in the US is that walkability invites social problems. So to have good cities, you must not tolerate social dysfunction. If you tolerate it, people will use car-dependent development to insulate themselves from it. At least, that seems to be what's happened.