In regards to the original question,
"Is it possible to say that the best tobaccos of previous decades were superior to the best of what's out there now?", also consider that, as a general rule, of the millions of pounds of tobacco produced each year by growers all over the world, the tobacco selected for pipes (and of course cigars) is the best of the lot, with the rest being churned into the cigarette and ancillary industries. So, as a baseline, pipe tobacco starts as the best of the best...of each crop, each year.
I would guess that in general, modernization and advances in agricultural science would have trended to improve crop quality overall since "the old days"; that said, each acre grown experiences a unique mixture of variables that make some years better or worse than others. So a short answer would be no; in general, tobacco
quality has
slightly improved
overall in the period between 1900-2022. That said, there are always outlier crops of exceptional quality when the magic of terroir and kismet combine in just the right way.
But that's just one tiny part of the equation. Much of what makes a finished blend is in the hands of the producer, and right now we're in the midst of a decade-plus long uptrend in the market (forecast to continue at least through 2027); increased demand has increased quality, variety, and quantity. That's just business.
I would love to hear blenders and buyers chime in on the quality of product and availability year-over-year (and decade-over-decade) in the trade markets. Russ! Greg! Ted! Per! I invoke ye!
But...
Then there's time. Once a blender has their way with a pile of leaf, and makes something truly special, then seals it away in a time capsule, magical eldritch things happen that can't be calculated or replicated. Aged tins of great blends that have proven their quality while fresh are, like wines of special vintage, paragons of gustatory experience, and sought after for good reason. Special crops like a 1983 Carolina red Virginia that someone had the foresight to mellow out, press into a cake, then tin up a decade later--you can't replicate that experience any other way.
Interestingly posed question that really has me pondering, thank you
@pauls456