Yeah, the labor standards that existed in the pre 2000s are vastly different to how divided and diverse labor is today. There is a clear divide in labor between what one would see as "youth labor" not highschoolers but younger people working in non traditional labor settings (Starbucks, Whole Foods, Amazon, etc), these individuals are most commonly politically opposed to the usual political leanings of "older insular labor" these are the old unions filled with mainly male workers (commonly older and conservative) who have at best "traditional democratic" values and at worst are chuds in everything but name. The Teamsters, though they may have younger members, are a traditionally male and older worker union that sadly has a lot of trappings preserved from the 1960s-70s with no clear coherent understanding or unwillingness to understand historically what has been done to labor unions over the last four decades (or they just don't give a shit).

I’ll give him the benefit of the doubt for thinking of a plan to have a successful revolution in America, but winning over the teamsters to help form a vanguard party (especially on the ideas of internationalism) to me feels as fantastical as a communist winning the presidency and dismantling the empire from the inside.

Yes. Communism doesn’t mean exploitation no longer exists, it just means you seek to reduce it as much as possible. Inequality will always exists, and it can be as local as your manager forcing you to work uncompensated overtime without knowledge or consent from the party or government. You can have all the communist laws and theories, but you still need people to make sure those laws and theories are understood and practiced. Shitty management will exist regardless of ideology because not everyone is cut out for it.