I started shooting just as plastic one piece wads were starting to be the norm. I am the "numbah one cheap Charlie", so I have shot hundreds of factory and handloaded card wads. All the problems I remember reading about with "shot lumps" were black powder loads with very soft shot. Could lead oxidization cause shot to stick together in a lump? I suppose it's possible. I don't use card OP wads by themselves much. I use old Alcan PGS or Air-Wedge or BPI's obturators with a card over them (mostly to prevent powder migration). A lot of older guns were choked for card wads and are tight with plastic one piece wads. Card loads without shot cups will let an extra tight choke pattern to it's original boring. However, loading card and fillers is a big hassle and I don't load a lot of them for target practice.
You and I started reloading at about the same time. (Getting to old geezers, ain't we?!)
Those were "gee whiz" days, weren't they! Man, the loads that some of us put together in those days! It is a testimonial to the guns that were used that more "MEC mechanics" ("Acme", in those days)did not end up with parts missing. In fairness, however, some of then loading data that we had and used would scare the pants off any competent reloader, today.
You still use PGSs and Air-Wedges? Wow! You ARE a hoarder! Those old wads might now be worth more a collectors' items than they might be as reloading components.
I must say that I am a bit of an agnostic when it comes to old guns shooting "tighter" with plastic wad loads. One can certainly make a case for "denser" and/or more "center dense" in many cases. However, "tighter" also involves effective pattern diameter. While "old style" loads MIGHT throw wider effective patterns because of increaed shot deformation at least as often the deformed shot "goes cattywumpus".