Ugh, my senior is such a jerk

Typical small company life
It's just a two-person team consisting of my senior and me
The senior has some experience, and I'm a rookie with less than a year under my belt
While computer-based tasks are important, there are also many tasks that require physical manual labor
My senior is certainly good at their job, but
They completely dodge all the tasks that require manual labor
A task that would take 30 minutes to an hour if we did it together
They leave it entirely to me, and it takes me two hours
I'm working overtime every single day
While they leave exactly on time or leave an hour or two early
Of course, they say things like, "I've gained enough seniority that I don't do this kind of work anymore"
I sort of understand, but at the same time, I don't
Does it actually hurt to do it together?
They could wrap it up in fancy words like "I'm entrusting this to you because I trust you,"
But no matter how much I think about it, I feel like it's fundamentally a character issue.