I don't see why guaranteed jobs need to be worse, it it out of fear that it will reduce the supply of workers in the private sector? Government jobs can provide a floor on pay and conditions, it doesn't have to be a race to the bottom that the government needs to make sure they treat their workers worse than the worst private employer.
As far as choosing between welfare and a job guarantee, there are inherent benefits to working even with the same pay, and jobs could be paid at a higher level than welfare, which encourages participation