It's not just "on average", people are materially better off today than at any other period in history, at all levels. The poorest people today are better off than the poorest people at any previous era.
That hasn't changed. If you're referring to the poorest in your particular nation state, consider they're probably not the poorest in the world, which we're all using in some way.
I don't think I have an overly rosy picture of the present. Rather I think your picture of the past is too romantic.
There are more people (in real numbers) starving than ever before. Looking at this in terms of percentages is misleading
Um, per capita is the important metric.
If there are 2 million people on your planet and 1 million of them are starving, then in a few generations there 100 million people and 2 million of them are starving you have drastically reduced the rate of starvation. Malthusian predictions of the past have said that the rate of starvation/bad things happening would increase as the population increased. It has not.
The true number of starving people is not an important metric?
Also material betterment doesn't scale, we can't focus on material betterment for all because until we figure out fusion and get our own Dyson Sphere going, we have finite resources.
Is this actually established? It's my understanding that the work-leisure dichotomy didn't really exist in medieval Europe. Also, considering how much of the fruit of your labour ended up supporting local and distant aristocracy, I can't imagine mental health being particularly high for a lot of people.
* For source, I've seen Yuval Noah Harari and Peter Gray writing about it.
As Oscar Wilde put it:
Now and then, in the course of the century, a great man of science, like Darwin; a great poet, like Keats; a fine critical spirit, like M. Renan; a supreme artist, like Flaubert, has been able to isolate himself, to keep himself out of reach of the clamorous claims of others, to stand ‘under the shelter of the wall,’ as Plato puts it, and so to realise the perfection of what was in him, to his own incomparable gain, and to the incomparable and lasting gain of the whole world. These, however, are exceptions. The majority of people spoil their lives by an unhealthy and exaggerated altruism – are forced, indeed, so to spoil them. They find themselves surrounded by hideous poverty, by hideous ugliness, by hideous starvation.