You're not exactly reading that correctly. What was compared was shot suitable for older barrels, not "the best No-Tox." Hevi-Shot is just a brand, not a specific
It was Hevi-Shot Classic Doubles that was compared to Kent TM. The density varies all over the place, with Hevi-13 and Dead Coyote heavier than lead, but most of the other "Hevi-Shot" isn't all that heavy and is not as dense as lead nor as dense as Kent TM. Hevi-Shot "Pheasant" is another one of the really poor Hevi-Shots, particularly considering the anemic payload of just 7/8 oz. in 20 gauge. The Classic Doubles in a 3 inch 20 gauge shell is still 1 oz. @ 1150 fps.
A Kent TM 3 in. 20 gauge is 1-1/8 oz. @ 1360 fps and it drops pheasants stone dead past 40 yards. No comparison on the patterning board or in the field.
This is a rooster that hit the air towards the end of the day just yesterday: