Right, I think this is a good point. After the devastation of World War II, Attlee successfully used government intervention to build an economy out of ruin, and established Britain's "cradle to grave" welfare state that continues to lift millions of out squalor every single year. The Attlee government also nationalized and rebuilt key industries, and had the Bank of England reinvigorate Britain's economy by embracing Keynesian crisis policy.
Under Attlee's leadership, the Labour Party took up the Beveridge Report in its manifesto, and established the National Health Service, Britain's extremely successful system of socialized healthcare. To this day, Britain's single-payer system is far more cost-effective than America's convoluted healthcare system.
Attlee, a self-described democratic socialist (albeit he governed as a social democrat), gave Britain the NHS, expansion of national insurance, raising of state pensions, unemployment benefits, child benefits, maternity benefits, sickness benefits, expansion of war pensions for the wounded and widowed. Infant mortality went down, life expectancy went up. Universal family allowances were introduced. Furthermore workers rights were expanded upon; entitlement to sick leave was increased, workers compensation was increased and much more.
When William Churchill became Prime Minister again in 1951, he did not dare undo Attlee's domestic reforms. In fact, until the 1980s, both Tory and Labour governments adhered to the "post-war consensus," in which the government maintained full unemployment via Keynesian policies, with the UK staying on the hard-left of social democracy until Margaret Thatcher almost completely obliterated it in the 1980s.
It wasn't until the late 1980s and 1990s that Labour embraced neoliberalism and moved toward the "Third Way." This was after Britain's welfare state was well established and entrenched, with Tony Blair wanting to "modernize" the federal government while making it more enterprise-friendly, smaller, and agile in light of a newly globalized era.
The existing welfare states and social-democratic structures of European countries were crafted and built prior to the 1970s, and were made more efficient after that. As a result, if we're focusing on change, the type of fundamental change Sanders is talking about (single-payer healthcare), it's not wrong at all to look at the ways politicians like Olof Palme, Clement Attlee, and others fundamentally transformed the political-economic structures of their countries and what lessons we can draw from those.