Regarding 1 and 2-irons, I reckon quite a bit of the trajectory issue has to do with the modern generation ball.
With a balata ball you could get a higher trajectory from a 1 or 2-iron. The modern generation ball doesn't spin in the same way so doesn't seem go as high with 1 and 2-irons. Just MO. Plus there's an element of maintenace/weather involved in that 1 and 2-irons are generally more of a F&F ground game - windy track based club and were maybe never really that suited to softer-lusher courses which have become a bit more prominent over the period since balata was phased out.
Good point about the newer size drivers Doug. A 1-iron used to be a regular lay-up club for me but the modern 460cc driver is relatively easy to hit so there's now less need to lay-up. An old wooden driver with a steel shaft used to be just about the hardest club in the bag to hit well, hence lay-ups with 1-irons. Now, the jumbo headed 460cc driver may debatably be the easiest to hit club in the bag.
ATB
I agree 100% with what you say about the balata ball being a big difference. The new ball is expressly designed to spin less at a higher impact speed, and a 1 iron is a pretty long club, so there's little doubt a longer hitter would see less backspin off a 1 iron using a Pro V1 than the Tour Balata or even the Professional used to get. That's not to say that age related decline in swing speed isn't a possible factor as well, that will turn the best of us into short knockers eventually, and short knockers have no use for a 1 iron!
I've been saying the same thing about the big drivers. Back in the days before metal woods, being able to hit a driver well was the mark of a good player, because it was the most difficult club in the bag to master. Now it is the easier club to hit, by far. Before the big drivers appeared, I was deadly off the tee with my 1 iron, able to hit it about 260 versus maybe 280 with my driver (some days better, some days worse, you know how it goes) The 1 iron was almost always straighter and more consistently struck and a lot of people wondered why I even bothered with my driver. I often wondered myself, and there were days I'd be hitting 1 iron on pretty much every hole, even the long par 5s
The Pro V1 definitely changed that, by making really bad outcomes for the driver less likely and increasing distance with it without really affecting my 1 iron distance off the tee at all (I still don't understand how the pros started hitting 5 irons 230 with the Pro V1, I used to hit my irons as far as the longest pros, but gained maybe 5 yards with my irons from the Pro V1, nothing like what some of them did)