The Nelson class was strong but too slow

Were Nelson and Rodney among the worst treaty-compromise battleships?

No; they were strongly armed and protected, but insufficient speed prevented an otherwise excellent design from reaching its potential.

The Nelsons were capable treaty battleships, with strong protection and 16-inch guns. Their wartime performance shows that the light-shell gun choice did not make them ineffective. Their chief compromise was speed, made more conspicuous because the ships were already over a decade old when war began. Using the remaining treaty allowance, accepting a slight tonnage fudge, and rearranging weight could have produced a 25-knot ship or perhaps a 28-knot early fast battleship.