“still hinges on being able to successfully advertise oneself”
Ever heard of friends and connections?

“mode of operation required by the market”
Everyone fits into factory work (manufacturing) and customer support.

“then there are artists who simply never get the recognition they deserve in their lifetime”
Nobody forced you to be an artist. Do what pays you better.

“those who just don't have any of the talents the market is looking for”
They work in factories, restaurants, logistics (delivery guys, drivers etc.). By the way, these jobs are driven away by social democrats in the name of oppression. If the people working there feel oppressed, they’re always free to leave. What’s the point of driving away those jobs. Most of the day to day goods are expensive because of the taxes and hyperinflation introduced by socialists or social democrats.

“be aware that you're talking to a social democrat.”
The economics is not much different. The level of central planning (socialism) is still too high to be sustainable for an environment that produces growth.

“I'm championing a mixed economy approach with regulations, public utilities, publicly financed education and generous welfare measures (e.g. universal healthcare, guaranteed housing, UBI, etc).”
These are nowhere close to being generous. In fact these things are terribly destructive for the economy. Not only are they extremely expensive and wasteful, but they also create shortages and random distribution. All of the meaningful and focused research in healthcare and other sciences comes from companies that understand their customers and what needs to be done. Most of the papers published by universities are nothing short of crap and have terrible amounts of left wing bias, to the point that some of the statistical ones are even false. It makes no sense to fund these things with public money. Companies are much more informed and efficient at investing than government. As far as housing is concerned, why should the government subsidise those companies that hire low skilled workers by bearing the cost of housing. If there was no free housing and regulations/taxes on builders and companies that hire low skilled workers, companies would be paying enough for their employees to survive (which requires them to live in a home). In fact, companies build housing themselves right next to the factory to save up on time. This can be seen with zowee in Shenzhen, where they have libertarian economic policies in place.