See, maybe this is just a cultural difference but I definitely know unionized people who have taken on responsibility outside their formal JD

And I've definitely heard of non unionised companies with rigid roles like that where the middle managers liked having defined roles with little room for taking on additional responsibilities.

The difference between the two IMO is if the union has shit representatives you _can_ work with colleagues to get a different union rep as it's democratic when implemented correctly, whereas with a crap management you only have the option of moving job, so at least with a more unionised workforce you can do both.