That does happen, and that junior level work is constructive, but what I've also experienced and noticed is that companies put a lot of effort into finding and hiring exceptionally skilled juniors (industrial placement schemes, graduate fast-tracks, etc.) where they can make safe bets on those people delivering significant value to their companies/projects. Some bigger companies do make an effort to build a mutually beneficial working relationship with a clear 5 year career roadmap (some sectors really struggle with those best candidates choosing FinTech instead). I've worked with high-performing junior programmers that have (quantitatively and qualitatively) dramatically outperformed experienced mid-level programmers, so I'm always an advocate for investing in them.

This is often win-win as the junior ends up with a robust list of resume bullets that help push their career forward.