I feel you missed a key part of the essay;
"From the beginning of civilization until the industrial revolution a man could, as a rule, produce by hard work little more than was required for the subsistence of himself and his family [..] Much that we take for granted about the desirability of work is derived from this system"
Lord Russell is praising the kind of hard work your father and grandfather did, that work is the cause of everyone considering work a virtue in itself. Rather, it is the system where millionaires and billionaires, oil barons and railway tycoons, landlords and ladies sail over the 'depression' untouched, when tractors and factory engines were boosting productivity, and still the working classes were working dawn to dusk for basic survival, much of the value of their work accruing to others and supporting government arms, and them being told it was all OK because of the inherent virtue of 'work', he criticises.
"and, being pre-industrial, is not adapted to the modern world. Modern technic has made it possible for leisure, within limits, to be not the prerogative of small privileged classes, but a right evenly distributed throughout the community."
He admits leisure is a perogative of privileged classes, while you criticise his essay on the grounds that he is privileged; but he argues that it shouldn't be a privileged position, it should be everybody's chance to benefit from industrialisation and automation, and not have to work dawn to dusk when others don't have to.