I use 12lb mainline and pva bags without a shockleader with no problems, I tend not to fish pva bags at range anyway as they can reduce my accuracy. When beachcasting, I would often use leads in the 4-6oz range and the casting style would demand a shockleader as the forces imposed on the mainline by the rods t/c, the actual casting style, (half pendulum, full pendulum, OTC, etc) and the added weight of a baited 2-3 hook trace, or a mackerel fillet or peeler crab etc, the initial air resistance of the baited end tackle, not forgetting the hostile nature of the sea to begin with, all these factors place a far greater strain on a mainline used for beachcasting than the strain placed in a carping environment.
most modern carp lines snap at a higher strain than their stated breaking strain, and most modern set ups can, in the right hands, put a 3oz lead a long way with little force or effort. I’ve had a rod fail before the mainline when casting extreme range (twice!) it’s a case of being sensible, I’m happy to blast a 3 1/2oz lead as far as I can chuck it with 15lb line, if I was using a lower b/s line, of 10lb say, I’d use a length of 20lb line as a shockleader, or if it was a common tactic, if fishing a water where extreme range fishing was the norm, I would turn to a tapered mainline. (I would also use these on waters where leaders are banned) but to be honest, I haven't needed a shockleader for years, diawa hypersensor has reduced diameter for its b/s so I can use a line of 15-18lb with a line diameter of 12lb(ish) modern mainlines give us more options these days