I don’t see that it’s ‘boasting’ to send charity cards, Grandtante - TBH that’s never occurred to me. If you’re going to send cards anyway, why not?
As for Christmas letters, or round robins as they’re often called, I think they did fall partly out of favour because too many of them turned into brag-fests about children’s achievements, their wonderful lifestyle/holidays, etc. Nobody ever sent one saying that they’d put on 3 stone and their eldest failed most of their GCSEs! (At least, not that I ever saw.).
Another kind we still get is from a far flung Canadian relative of dh who TBH we barely know - 2 x A4 pages in a tiny font, crammed with news of her doings and ailments, and news of a lot of people we either don’t know at all, or hardly at all - and all their doings and ailments.
I’d rather have a few lines scribbled inside the card, but that’s obviously rather more of a faff than the same thing photocopied for everybody.