Very interesting question. In my opinion, except for the advancement in slugs, and barrels for long range shooting, I do not think they are. A 10m gun would probably shoot one hole twenty year ago, as now.
What probably has improved, is the selection, and quality of pellets, and the ease of tuning of some guns. And the most important thing: On internet early days, there was limited information on how to properly tune a gun. The information available was probably for professionals, and manufacturers. Now allot of information is available and shared by everyone, like this forum. Meaning most average Joe`s can be a decent tuner with some patience, getting the best performance of their guns.