It's more of a case of there WERE some 20mm weapons that could fall into LAG territory, the Swiss Solothurn being the best of the bunch. All were designed as man-portible anti-tank rifles, being used later as anti-sniping weapons after newer tanks became immune to them. Today's .50 cal rifles infact take the .50 cal cartridge back to it's origins as a large-bore, man-portable munition. The Barrett of todays owes much to the German designers that came up with it tword the end of WW1. It took the genius of John Browning to think of designing a machine gun to use this beast of a cartridge. The larger Russian round followed pretty nuch the same path.
So if Traveller erred at all with the LAG concept it was by not placing them early enough. It can still have a role in the post RAM/Bazooka eras, just very different from what their designers might have had in mind.
