That might be true in terms of CO2 and energy efficiency, although the only sources i've found on the topic gave very opposite results. But no study that i know of accounts for pollution (waste water and polluted surroundings of extraction sites, refinement sites, assembly sites, and "recycling" sites) so i'm tempted to argue that anything we don't manufacture is better for the environment than better efficiency.
> The lack of appliances that last this long is itself a result of better production: if you have some large number of components, each one must have a 50 year expected lifetime if you want a chance for the machine to work for even a decade.
I strongly disagree with this interpretation. First, because industry routinely employs bad parts and bad design on purpose (planned obsolescence, eg. televisions placing heat-sensitive capacitors near heat sources). But also because an individual part failing is in my view OK as long as this part is standard and easy to source.
There are some environmental/logistic concerns if you want to repair old devices given the gazillion incompatible spare parts they each use. But if they all used standard parts, we could and should have repair shops run as a free public service to avoid throwing stuff away. This in itself would do more for the environment than any "green new deal" would ever do.