> they’re speaking up for working people
No, they're not, they're speaking up for some working people, i.e. their members. Most working people are not their members. Somebody working for a small business (in an office or a shop or a warehouse or a workshop or on the road) has very little in common workwise with their members. Mick Lynch et al does not speak for such people.
As for Labour, it should do what it wants, not what somebody else wants, and that seems to me exactly what Starmer is doing. Just because a union leader thinks something, doesn't mean that Labour blindly agrees. You can't keep everybody happy, especially when not everybody has the same opinion about something - you have to do things your way. That is leadership.