While we may be overproducing in some specific fields, there are many places we are not producing/developed enough (green energy and infrastructure are prime examples) especially if you begin to account for national boundaries and ending imperialism. We've also got to bring something like 15 million people into the workforce (whatever the unemployment is) while also ending one of the major inefficiencies of capitalism which is unnecessary competition, which will eliminate some jobs. We do this by further dividing labor and reducing the hours worked (which can only be done if someone is able to live on the reduced hours ergo we socialize things like medical care, education, housing, food, utilities, etc., which in turn also creates more jobs. We need to rapidly change the economy primarily for climate change but for other reasons as well and this entails further development of the means of production and division of labor even though we are significantly more advanced than the economies of Marx's time. In essence while we are a fully developed capitalist economy, the antagonistic contradictions with the capitalist economy prevent it from providing what is necessary so we must replace the capitalist economy with a socialist one and develop from there.

As to the second part, Marx had kind of a narrow view of what the proletariat was and within his time and place it was kind of (politically) homogeneous in part due to the organization of the trade unions. Depending on your reading he also thought the proletariat was the only revolutionary class in capitalist society which history has proven incorrect. You sometimes see those ideas reiterated in leftest spaces and adhering to this position creates a problems if you're looking at democratic socialism (i.e. the DSA) in the US which is generally white and well educated (I think it tends male as well but I'm not certain about that). If you look at revolutions historically however, they are composed of multiple classes, different ideologies, and were multi-racial where that is applicable. I think Lenin excellently states what the goal should be in What is to Be Done:

if “we” desire to be front-rank democrats, we must make it our concern to direct the thoughts of those who are dissatisfied only with conditions at the university, or in the Zemstvo, etc., to the idea that the entire political system is worthless. We must take upon ourselves the task of organising an all-round political struggle under the leadership of our Party in such a manner as to make it possible for all oppositional strata to render their fullest support to the struggle and to our Party. We must train our Social-Democratic practical workers to become political leaders, able to guide all the manifestations of this all-round struggle, able at the right time to “dictate a positive programme of action” for the aroused students, the discontented Zemstvo people, the incensed religious sects, the offended elementary schoolteachers, etc., etc.

Now obviously we have no Zemstvo (sort of a weak regional legislature) liberals to organize but our goal should be to identify the varying sections in society and lead them to revolution however possible. That might mean working with petty bourgeoisie, lumpen-proletarians, or the dreaded PMC. That might mean convincing self described "democratic" socialists or even liberals to be revolutionary. I think we need a revolution, but things certainly aren't ready for one so working within the framework of "democratic socialism" might be useful. We just need to remember the ultimate need for revolution.